The Student's Elements of Geology
Sir Charles Lyell
Part 3 out of 14
origin, thin out gradually as they are traced to the westward, where evidently
the contemporaneous seas allowed organic rocks to be formed by corals,
echinoderms, and encrinites in clearer water, and where, although the same
successive periods are represented, the total mass of strata from the Silurian
to the Carboniferous, instead of being 40,000 is only 4000 feet thick.
A like phenomenon is exhibited in every mountainous country, as, for example, in
the European Alps; but we need not go farther than the north of England for its
illustration. Thus in Lancashire and central England the thickness of the
Carboniferous formation, including the Millstone Grit and Yoredale beds, is
computed to be more than 18,000 feet; to this we may add the Mountain Limestone,
at least 2000 feet in thickness, and the overlying Permian and Triassic
formations, 3000 or 4000 feet thick. How then does it happen that the loftiest
hills of Yorkshire and Lancashire, instead of being 24,000 feet high, never rise
above 3000 feet? For here, as before pointed out in the Alleghenies, all the
great thicknesses are sometimes found in close approximation and in a region
only a few miles in diameter. It is true that these same sets of strata do not
preserve their full force when followed for indefinite distances. Thus the
18,000 feet of Carboniferous grits and shales in Lancashire, before alluded to,
gradually thin out, as Mr. Hull has shown, as they extend southward, by
attenuation or original deficiency of sediment, and not in consequence of
subsequent denudation, so that when we have followed them for about 100 miles
into Leicestershire, they have dwindled away to a thickness of only 3000 feet.
In the same region the Carboniferous limestone attains so unusual a thickness--
namely, more than 4000 feet-- as to appear to compensate in some measure for the
deficiency of contemporaneous sedimentary rock. (Hull Quarterly Geological
Journal volume 24 page 322 1868.)
(FIGURE 82. Unconformable Palaeozoic strata, Sutherlandshire (Murchison).
Queenaig (2673 feet).
1. Laurentian gneiss.
2. Cambrian conglomerate and sandstone.
3, 3'. Quartzose Lower Silurian, with annelid burrows.)
It is admitted that when two formations are unconformable their fossil remains
almost always differ considerably. The break in the continuity of the organic
forms seems connected with a great lapse of time, and the same interval has
allowed extensive disturbance of the strata, and removal of parts of them by
denudation, to take place. The more we extend our investigations the more
numerous do the proofs of these breaks become, and they extend to the most
ancient rocks yet discovered. The oldest examples yet brought to light in the
British Isles are on the borders of Rosshire and Sutherlandshire, and have been
well described by Sir Roderick Murchison, by whom their chronological relations
were admirably worked out, and proved to be very different from those which
previous observers had imagined them to be. I had an opportunity in the autumn
of 1869 of verifying the splendid section given in Figure 82 by climbing in a
few hours from the banks of Loch Assynt to the summit of the mountain called
Queenaig, 2673 feet high.
The formations 1, 2, 3, the Laurentian, Cambrian, and Silurian, to be explained
in Chapters 25 and 26, not only occur in succession in this one mountain, but
their unconformable junctions are distinctly exposed to view.
To begin with the oldest set of rocks, No. 1; they consist chiefly of
hornblendic gneiss, and in the neighbouring Hebrides form whole islands,
attaining a thickness of thousands of feet, although they have suffered such
contortions and denudation that they seldom rise more than a few hundred feet
above the sea-level. In discordant stratification upon the edges of this gneiss
reposes No. 2, a group of conglomerate and purple sandstone referable to the
Cambrian (or Longmynd) formation, which can elsewhere be shown to be
characterised by its peculiar organic remains. On this again rests No. 3, a
lower member of the important group called Silurian, an outlier of which, 3',
caps the summit of Queenaig, attesting the removal by denudation of rocks of the
same age, which once extended from the great mass 3 to 3'. Although this rock
now consists of solid quartz, it is clear that in its original state it was
formed of fine sand, perforated by numerous lob-worms or annelids, which left
their burrows in the shape of tubular hollows (Chapter 26, Figure 563 of
Arenicolites), hundreds, nay thousands, of which I saw as I ascended the
(FIGURE 83. Diagrammatic section of the same groups near Queenaig (Murchison)
through west (left), Suilvein, Assynt and Ben More, east (right).
1. Laurentian gneiss.
2. Cambrian conglomerate and sandstone.
3, 3'. Quartzose Lower Silurian, with annelid burrows.
3a. Fossiliferous Silurian limestone.
3b. Quartzose, micaceous and gneissose rocks (altered Silurian).)
In Queenaig we only behold this single quartzose member of the Silurian series,
but in the neighbouring country (see Figure 83) it is seen to the eastward to be
followed by limestones, 3a, and schists, 3b, presenting numerous folds, and
becoming more and more metamorphic and crystalline, until at length, although
very different in age and strike, they much resemble in appearance the group No.
1. It is very seldom that in the same country one continuous formation, such as
the Silurian, is, as in this case, more fossiliferous and less altered by
volcanic heat in its older than in its newer strata, and still more rare to find
an underlying and unconformable group like the Cambrian retaining its original
condition of a conglomerate and sandstone more perfectly than the overlying
formation. Here also we may remark in regard to the origin of these Cambrian
rocks that they were evidently produced at the expense of the underlying
Laurentian, for the rounded pebbles occurring in them are identical in
composition and texture with that crystalline gneiss which constitutes the
contorted beds of the inferior formation No. 1. When the reader has studied the
chapter on metamorphism, and has become aware how much modification by heat,
pressure, and chemical action is required before the conversion of sedimentary
into crystalline strata can be brought about, he will appreciate the insight
which we thus gain into the date of the changes which had already been effected
in the Laurentian rocks long before the Cambrian pebbles of quartz and gneiss
were derived from them. The Laurentian is estimated by Sir William Logan to
amount in Canada to 30,000 feet in thickness. As to the Cambrian, it is supposed
by Sir Roderick Murchison that the fragment left in Sutherlandshire is about
3500 feet thick, and in Wales and the borders of Shropshire this formation may
equal 10,000 feet, while the Silurian strata No. 3, difficult as it may be to
measure them in their various foldings to the eastward, where they have been
invaded by intrusive masses of granite, are supposed many times to surpass the
Cambrian in volume and density.
But although we are dealing here with stratified rocks, each of which would be
several miles in thickness, if they were fully represented, the whole of them do
not attain the elevation of a single mile above the level of the sea.
COMPUTATION OF THE AVERAGE ANNUAL AMOUNT OF SUBAERIAL DENUDATION.
The geology of the district above alluded to may assist our imagination in
conceiving the extent to which groups of ancient rocks, each of which may in
their turn have formed continents and oceanic basins, have been disturbed,
folded, and denuded even in the course of a few out of many of those geological
periods to which our imperfect records relate. It is not easy for us to
overestimate the effects which causes in every day action must produce when the
multiplying power of time is taken into account.
Attempts were made by Manfredi in 1736, and afterwards by Playfair in 1802, to
calculate the time which it would require to enable the rivers to deliver over
the whole of the land into the basin of the ocean. The data were at first too
imperfect and vague to allow them even to approximate to safe conclusions. But
in our own time similar investigations have been renewed with more prospect of
success, the amount brought down by many large rivers to the sea having been
more accurately ascertained. Mr. Alfred Tylor, in 1850, inferred that the
quantity of detritus now being distributed over the sea-bottom would, at the end
of 10,000 years, cause an elevation of the sea-level to the extent of at least
three inches. (Tylor Philosophical Magazine 4th series page 268 1850.)
Subsequently Mr. Croll, in 1867, and again, with more exactness, in 1868,
deduced from the latest measurement of the sediment transported by European and
American rivers the rate of subaerial denudation to which the surface of large
continents is exposed, taking especially the hydrographical basin of the
Mississippi as affording the best available measure of the average waste of the
land. The conclusion arrived at in his able memoir was that the whole
terrestrial surface is denuded at the rate of one foot in 6000 years (Croll
Philosophical Magazine 1868 page 381.), and this opinion was simultaneously
enforced by his fellow-labourer, Mr. Geikie, who, being jointly engaged in the
same line of inquiry, published a luminous essay on the subject in 1868.
The student, by referring to my "Principles of Geology" (Volume 1 page 442
1867.) may see that Messrs. Humphrey and Abbot, during their survey of the
Mississippi, attempted to make accurate measurements of the proportion of
sediment carried down annually to the sea by that river, including not only the
mud held in suspension, but also the sand and gravel forced along the bottom.
It is evident that when we know the dimensions of the area which is drained, and
the annual quantity of earthy matter taken from it and borne into the sea, we
can affirm how much on an average has been removed from the general surface in
one year, and there seems no danger of our overrating the mean rate of waste by
selecting the Mississippi as our example, for that river drains a country equal
to more than half the continent of Europe, extends through twenty degrees of
latitude, and therefore through regions enjoying a great variety of climate, and
some of its tributaries descend from mountains of great height. The Mississippi
is also more likely to afford us a fair test of ordinary denudation, because,
unlike the St. Lawrence and its tributaries, there are no great lakes in which
the fluviatile sediment is thrown down and arrested in its way to the sea. In
striking a general average we have to remember that there are large deserts in
which there is scarcely any rainfall, and tracts which are as rainless as parts
of Peru, and these must not be neglected as counterbalancing others, in the
tropics, where the quantity of rain is in excess. If then, argues Mr. Geikie, we
assume that the Mississippi is lowering the surface of the great basin which it
drains at the rate of one foot in 6000 years, 10 feet in 60,000 years, 100 feet
in 600,000 years, and 1000 feet in 6,000,000 years, it would not require more
than about 4,500,000 years to wear away the whole of the North American
continent if its mean height is correctly estimated by Humboldt at 748 feet. And
if the mean height of all the land now above the sea throughout the globe is
1000 feet, as some geographers believe, it would only require six million years
to subject a mass of rock equal in volume to the whole of the land to the action
of subaerial denudation. It may be objected that the annual waste is partial,
and not equally derived from the general surface of the country, inasmuch as
plains, water-sheds, and level ground at all heights remain comparatively
unaltered; but this, as Mr. Geikie has well pointed out, does not affect our
estimate of the sum total of denudation. The amount remains the same, and if we
allow too little for the loss from the surface of table-lands we only increase
the proportion of the loss sustained by the sides and bottoms of the valleys,
and vice versa. (Transactions of the Geological Society Glasgow volume 3 page
ANTAGONISM OF VOLCANIC FORCE TO THE LEVELLING POWER OF RUNNING WATER.
In all these estimates it is assumed that the entire quantity of land above the
sea-level remains on an average undiminished in spite of annual waste. Were it
otherwise the subaerial denudation would be continually lessened by the
diminution of the height and dimensions of the land exposed to waste.
Unfortunately we have as yet no accurate data enabling us to measure the action
of that force by which the inequalities of the surface of the earth's crust may
be restored, and the height of the continents and depth of the seas made to
continue unimpaired. I stated in 1830 in the "Principles of Geology" (1st
edition chapter 10 page 167 1830; see also 10th edition volume 1 chapter 15 page
327 1867.), that running water and volcanic action are two antagonistic forces;
the one labouring continually to reduce the whole of the land to the level of
the sea, the other to restore and maintain the inequalities of the crust on
which the very existence of islands and continents depends. I stated, however,
that when we endeavour to form some idea of the relation of these destroying and
renovating forces, we must always bear in mind that it is not simply by upheaval
that subterranean movements can counteract the levelling force of running water.
For whereas the transportation of sediment from the land to the ocean would
raise the general sea-level, the subsidence of the sea-bottom, by increasing its
capacity, would check this rise and prevent the submergence of the land. I have,
indeed, endeavoured to show that unless we assume that there is, on the whole,
more subsidence than upheaval, we must suppose the diameter of the planet to be
always increasing, by that quantity of volcanic matter which is annually poured
out in the shape of lava or ashes, whether on the land or in the bed of the sea,
and which is derived from the interior of the earth. The abstraction of this
matter causes, no doubt, subterranean vacuities and a corresponding giving way
of the surface; if it were not so, the average density of parts of the interior
would be always lessening and the size of the planet increasing. (Principles
volume 2 page 237; also 1st edition page 447 1830.)
Our inability to estimate the amount or direction of the movements due to
volcanic power by no means renders its efficacy as a land-preserving force in
past times a mere matter of conjecture. The student will see in Chapter 24 that
we have proofs of Carboniferous forests hundreds of miles in extent which grew
on the lowlands or deltas near the sea, and which subsided and gave place to
other forests, until in some regions fluviatile and shallow-water strata with
occasional seams of coal were piled one over the other, till they attained a
thickness of many thousand feet. Such accumulations, observed in Great Britain
and America on opposite sides of the Atlantic, imply the long-continued
existence of land vegetation, and of rivers draining a former continent placed
where there is now deep sea.
It will be also seen in Chapter 25 that we have evidence of a rich terrestrial
flora, the Devonian, even more ancient than the Carboniferous; while on the
other hand, the later Triassic, Oolitic, Cretaceous, and successive Tertiary
periods have all supplied us with fossil plants, insects, or terrestrial
mammalia; showing that, in spite of great oscillations of level and continued
changes in the position of land and sea, the volcanic forces have maintained a
due proportion of dry land. We may appeal also to fresh-water formations, such
as the Purbeck and Wealden, to prove that in the Oolitic and Neocomian eras
there were rivers draining ancient lands in Europe in times when we know that
other spaces, now above water, were submerged.
HOW FAR THE TRANSFER OF SEDIMENT FROM THE LAND TO A NEIGHBOURING SEA-BOTTOM MAY
AFFECT SUBTERRANEAN MOVEMENTS.
Little as we understand at present the laws which govern the distribution of
volcanic heat in the interior and crust of the globe, by which mountain chains,
high table-lands, and the abysses of the ocean are formed, it seems clear that
this heat is the prime mover on which all the grander features in the external
configuration of the planet depend.
It has been suggested that the stripping off by denudation of dense masses from
one part of a continent and the delivery of the same into the bed of the ocean
must have a decided effect in causing changes of temperature in the earth's
crust below, or, in other words, in causing the subterranean isothermals to
shift their position. If this be so, one part of the crust may be made to rise,
and another to sink, by the expansion and contraction of the rocks, of which the
temperature is altered.
I can not, at present, discuss this subject, of which I have treated more fully
elsewhere (Principles volume 2 page 229 1868.), but may state here that I
believe this transfer of sediment to play a very subordinate part in modifying
those movements on which the configuration of the earth's crust depends. In
order that strata of shallow-water origin should be able to attain a thickness
of several thousand feet, and so come to exert a considerable downward pressure,
there must have been first some independent and antecedent causes at work which
have given rise to the incipient shallow receptacle in which the sediment began
to accumulate. The same causes there continuing to depress the sea-bottom, room
would be made for fresh accessions of sediment, and it would only be by a long
repetition of the depositing process that the new matter could acquire weight
enough to affect the temperature of the rocks far below, so as to increase or
diminish their volume.
PERMANENCE OF CONTINENTAL AND OCEANIC AREAS.
If the thickness of more than 40,000 feet of sedimentary strata before alluded
to in the Appalachians proves a preponderance of downward movements in
Palaeozoic times in a district now forming the eastern border of North America,
it also proves, as before hinted, the continued existence and waste of some
neighbouring continent, probably formed of Laurentian rocks, and situated where
the Atlantic now prevails. Such an hypothesis would be in perfect harmony with
the conclusions forced upon us by the study of the present configuration of our
continents, and the relation of their height to the depth of the oceanic basins;
also to the considerable elevation and extent sometimes reached by drift
containing shells of recent species, and still more by the fact of sedimentary
strata, several thousand feet thick, as those of central Sicily, or such as
flank the Alps and Apennines, containing fossil Mollusca sometimes almost wholly
identical with species still living.
I have remarked elsewhere (Principles volume 1 page 265 1867.) that upward and
downward movements of 1000 feet or more would turn much land into sea and sea
into land in the continental areas and their borders, whereas oscillations of
equal magnitude would have no corresponding effect in the bed of the ocean
generally, believed as it is to have a mean depth of 15,000 feet, and which,
whether this estimate be correct or not, is certainly of great profundity.
Subaerial denudation would not of itself lessen the area of the land, but would
tend to fill up with sediment seas of moderate depth adjoining the coast. The
coarser matter falls to the bottom near the shore in the first still water which
it reaches, and whenever the sea-bottom on which this matter has been thrown is
slightly elevated, it becomes land, and an upheaval of a thousand feet causes it
to attain the mean elevation of continents in general.
Suppose, therefore, we had ascertained that the triturating power of subaerial
denudation might in a given time-- in three, or six, or a greater number of
millions of years-- pulverise a volume of rock equal in dimensions to all the
present land, we might yet find, could we revisit the earth at the end of such a
period, that the continents occupied very much the same position which they held
before; we should find the rivers employed in carrying down to the sea the very
same mud, sand, and pebbles with which they had been charged in our own time,
the superficial alluvial matter as well as a great thickness of sedimentary
strata would inclose shells, all or a great part of which we should recognise as
specifically identical with those already known to us as living. Every geologist
is aware that great as have been the geographical changes in the northern
hemisphere since the commencement of the Glacial Period, there having been
submergence and re-emergence of land to the extent of 1000 feet vertically, and
in the temperate latitudes great vicissitudes of climate, the marine mollusca
have not changed, and the same drift which had been carried down to the sea at
the beginning of the period is now undergoing a second transportation in the
As when we have measured a fraction of time in an hour-glass we have only to
reverse the position of our chronometer and we make the same sand measure over
again the duration of a second equal period, so when the volcanic force has
remoulded the form of a continent and the adjoining sea-bottom, the same
materials are made to do duty a second time. It is true that at each oscillation
of level the solid rocks composing the original continent suffer some fresh
denudation, and do not remain unimpaired like the wooden and glass framework of
the hour-glass, still the wear and tear suffered by the larger area exposed to
subaerial denudation consists either of loose drift or of sedimentary strata,
which were thrown down in seas near the land, and subsequently upraised, the
same continents and oceanic basins remaining in existence all the while.
From all that we know of the extreme slowness of the upward and downward
movements which bring about even slight geographical changes, we may infer that
it would require a long succession of geological periods to cause the submarine
and supramarine areas to change places, even if the ascending movements in the
one region and the descending in the other were continuously in one direction.
But we have only to appeal to the structure of the Alps, where there are so many
shallow and deep water formations of various ages crowded into a limited area,
to convince ourselves that mountain chains are the result of great oscillations
of level. High land is not produced simply by uniform upheaval, but by a
predominance of elevatory over subsiding movements. Where the ocean is extremely
deep it is because the sinking of the bottom has been in excess, in spite of
interruptions by upheaval.
Yet persistent as may be the leading features of land and sea on the globe, they
are not immutable. Some of the finest mud is doubtless carried to indefinite
distances from the coast by marine currents, and we are taught by deep-sea
dredgings that in clear water at depths equalling the height of the Alps organic
beings may flourish, and their spoils slowly accumulate on the bottom. We also
occasionally obtain evidence that submarine volcanoes are pouring out ashes and
streams of lava in mid-ocean as well as on land (see Principles volume 2 page
64), and that wherever mountains like Etna, Vesuvius, and the Canary Islands are
now the site of eruptions, there are signs of accompanying upheaval, by which
beds of ashes full of recent marine shells have been uplifted many hundred feet.
We need not be surprised, therefore, if we learn from geology that the
continents and oceans were not always placed where they now are, although the
imagination may well be overpowered when it endeavours to contemplate the
quantity of time required for such revolutions.
We shall have gained a great step if we can approximate to the number of
millions of years in which the average aqueous denudation going on upon the land
would convey seaward a quantity of matter equal to the average volume of our
continents, and this might give us a gauge of the minimum of volcanic force
necessary to counteract such levelling power of running water; but to discover a
relation between these great agencies and the rate at which species of organic
beings vary, is at present wholly beyond the reach of our computation, though
perhaps it may not prove eventually to transcend the powers of man.
CHRONOLOGICAL CLASSIFICATION OF ROCKS.
Aqueous, Plutonic, volcanic, and metamorphic Rocks considered chronologically.
Terms Primary, Secondary, and Tertiary; Palaeozoic, Mesozoic, and Cainozoic
On the different Ages of the aqueous Rocks.
Three principal Tests of relative Age: Superposition, Mineral Character, and
Change of Mineral Character and Fossils in the same continuous Formation.
Proofs that distinct Species of Animals and Plants have lived at successive
Distinct Provinces of indigenous Species.
Great Extent of single Provinces.
Similar Laws prevailed at successive Geological Periods.
Relative Importance of mineral and palaeontological Characters.
Test of Age by included Fragments.
Frequent Absence of Strata of intervening Periods.
Tabular Views of fossiliferous Strata.
CHRONOLOGY OF ROCKS.
In the first chapter it was stated that the four great classes of rocks, the
aqueous, the volcanic, the Plutonic, and the metamorphic, would each be
considered not only in reference to their mineral characters, and mode of
origin, but also to their relative age. In regard to the aqueous rocks, we have
already seen that they are stratified, that some are calcareous, others
argillaceous or siliceous, some made up of sand, others of pebbles; that some
contain fresh-water, others marine fossils, and so forth; but the student has
still to learn which rocks, exhibiting some or all of these characters, have
originated at one period of the earth's history, and which at another.
To determine this point in reference to the fossiliferous formations is more
easy than in any other class, and it is therefore the most convenient and
natural method to begin by establishing a chronology for these strata, and then
to refer as far as possible to the same divisions, the several groups of
Plutonic, volcanic, and metamorphic rocks. Such a system of classification is
not only recommended by its greater clearness and facility of application, but
is also best fitted to strike the imagination by bringing into one view the
contemporaneous revolutions of the inorganic and organic creations of former
times. For the sedimentary formations are most readily distinguished by the
different species of fossil animals and plants which they inclose, and of which
one assemblage after another has flourished and then disappeared from the earth
In the present work, therefore, the four great classes of rocks, the aqueous,
Plutonic, volcanic, and metamorphic, will form four parallel, or nearly
parallel, columns in one chronological table. They will be considered as four
sets of monuments relating to four contemporaneous, or nearly contemporaneous,
series of events. I shall endeavour, in a subsequent chapter on the Plutonic
rocks, to explain the manner in which certain masses belonging to each of the
four classes of rocks may have originated simultaneously at every geological
period, and how the earth's crust may have been continually remodelled, above
and below, by aqueous and igneous causes, from times indefinitely remote. In the
same manner as aqueous and fossiliferous strata are now formed in certain seas
or lakes, while in other places volcanic rocks break out at the surface, and are
connected with reservoirs of melted matter at vast depths in the bowels of the
earth, so, at every era of the past, fossiliferous deposits and superficial
igneous rocks were in progress contemporaneously with others of subterranean and
Plutonic origin, and some sedimentary strata were exposed to heat, and made to
assume a crystalline or metamorphic structure.
It can by no means be taken for granted, that during all these changes the solid
crust of the earth has been increasing in thickness. It has been shown, that so
far as aqueous action is concerned, the gain by fresh deposits, and the loss by
denudation, must at each period have been equal (see Chapter 6); and in like
manner, in the inferior portion of the earth's crust, the acquisition of new
crystalline rocks, at each successive era, may merely have counterbalanced the
loss sustained by the melting of materials previously consolidated. As to the
relative antiquity of the crystalline foundations of the earth's crust, when
compared to the fossiliferous and volcanic rocks which they support, I have
already stated, in the first chapter, that to pronounce an opinion on this
matter is as difficult as at once to decide which of the two, whether the
foundations or superstructure of an ancient city built on wooden piles may be
the oldest. We have seen that, to answer this question, we must first be
prepared to say whether the work of decay and restoration had gone on most
rapidly above or below; whether the average duration of the piles has exceeded
that of the buildings, or the contrary. So also in regard to the relative age of
the superior and inferior portions of the earth's crust; we can not hazard even
a conjecture on this point, until we know whether, upon an average, the power of
water above, or that of heat below, is most efficacious in giving new forms to
The early geologists gave to all the crystalline and non-fossiliferous rocks the
name of Primitive or Primary, under the idea that they were formed anterior to
the appearance of life upon the earth, while the aqueous or fossiliferous strata
were termed Secondary, and alluviums or other superficial deposits, Tertiary.
The meaning of these terms, has, however, been gradually modified with advancing
knowledge, and they are now used to designate three great chronological
divisions under which all geological formations can be classed, each of them
being characterised by the presence of distinctive groups of organic remains
rather than by any mechanical peculiarities of the strata themselves. If,
therefore, we retain the term "primary," it must not be held to designate a set
of crystalline rocks some of which have been proved to be even of Tertiary age,
but must be applied to all rocks older than the secondary formations. Some
geologists, to avoid misapprehension, have introduced the term Palaeozoic for
primary, from palaion, "ancient," and zoon, "an organic being," still retaining
the terms secondary and tertiary; Mr. Phillips, for the sake of uniformity, has
proposed Mesozoic, for secondary, from mesos, "middle," etc.; and Cainozoic, for
tertiary, from kainos, "recent," etc.; but the terms primary, secondary, and
tertiary have the claim of priority in their favour, and are of corresponding
It may perhaps be suggested that some metamorphic strata, and some granites, may
be anterior in date to the oldest of the primary fossiliferous rocks. This
opinion is doubtless true, and will be discussed in future chapters; but I may
here observe, that when we arrange the four classes of rocks in four parallel
columns in one table of chronology, it is by no means assumed that these columns
are all of equal length; one may begin at an earlier period than the rest, and
another may come down to a later point of time, and we may not be yet acquainted
with the most ancient of the primary fossiliferous beds, or with the newest of
For reasons already stated, I proceed first to treat of the aqueous or
fossiliferous formations considered in chronological order or in relation to the
different periods at which they have been deposited.
There are three principal tests by which we determine the age of a given set of
strata; first, superposition; secondly, mineral character; and, thirdly, organic
remains. Some aid can occasionally be derived from a fourth kind of proof,
namely, the fact of one deposit including in it fragments of a pre-existing
rock, by which the relative ages of the two may, even in the absence of all
other evidence, be determined.
The first and principal test of the age of one aqueous deposit, as compared to
another, is relative position. It has been already stated, that, where strata
are horizontal, the bed which lies uppermost is the newest of the whole, and
that which lies at the bottom the most ancient. So, of a series of sedimentary
formations, they are like volumes of history, in which each writer has recorded
the annals of his own times, and then laid down the book, with the last written
page uppermost, upon the volume in which the events of the era immediately
preceding were commemorated. In this manner a lofty pile of chronicles is at
length accumulated; and they are so arranged as to indicate, by their position
alone, the order in which the events recorded in them have occurred.
In regard to the crust of the earth, however, there are some regions where, as
the student has already been informed, the beds have been disturbed, and
sometimes extensively thrown over and turned upside down. (See Chapter 5.) But
an experienced geologist can rarely be deceived by these exceptional cases. When
he finds that the strata are fractured, curved, inclined, or vertical, he knows
that the original order of superposition must be doubtful, and he then
endeavours to find sections in some neighbouring district where the strata are
horizontal, or only slightly inclined. Here, the true order of sequence of the
entire series of deposits being ascertained, a key is furnished for settling the
chronology of those strata where the displacement is extreme.
The same rocks may often be observed to retain for miles, or even hundreds of
miles, the same mineral peculiarities, if we follow the planes of
stratification, or trace the beds, if they be undisturbed, in a horizontal
direction. But if we pursue them vertically, or in any direction transverse to
the planes of stratification, this uniformity ceases almost immediately. In that
case we can scarcely ever penetrate a stratified mass for a few hundred yards
without beholding a succession of extremely dissimilar rocks, some of fine,
others of coarse grain, some of mechanical, others of chemical origin; some
calcareous, others argillaceous, and others siliceous. These phenomena lead to
the conclusion that rivers and currents have dispersed the same sediment over
wide areas at one period, but at successive periods have been charged, in the
same region, with very different kinds of matter. The first observers were so
astonished at the vast spaces over which they were able to follow the same
homogeneous rocks in a horizontal direction, that they came hastily to the
opinion, that the whole globe had been environed by a succession of distinct
aqueous formations, disposed round the nucleus of the planet, like the
concentric coats of an onion. But, although, in fact, some formations may be
continuous over districts as large as half of Europe, or even more, yet most of
them either terminate wholly within narrower limits, or soon change their
lithological character. Sometimes they thin out gradually, as if the supply of
sediment had failed in that direction, or they come abruptly to an end, as if we
had arrived at the borders of the ancient sea or lake which served as their
receptacle. It no less frequently happens that they vary in mineral aspect and
composition, as we pursue them horizontally. For example, we trace a limestone
for a hundred miles, until it becomes more arenaceous, and finally passes into
sand, or sandstone. We may then follow this sandstone, already proved by its
continuity to be of the same age, throughout another district a hundred miles or
more in length.
This character must be used as a criterion of the age of a formation, or of the
contemporaneous origin of two deposits in distant places, under very much the
same restrictions as the test of mineral composition.
First, the same fossils may be traced over wide regions, if we examine strata in
the direction of their planes, although by no means for indefinite distances.
Secondly, while the same fossils prevail in a particular set of strata for
hundreds of miles in a horizontal direction, we seldom meet with the same
remains for many fathoms, and very rarely for several hundred yards, in a
vertical line, or a line transverse to the strata. This fact has now been
verified in almost all parts of the globe, and has led to a conviction that at
successive periods of the past, the same area of land and water has been
inhabited by species of animals and plants even more distinct than those which
now people the antipodes, or which now co-exist in the arctic, temperate, and
tropical zones. It appears that from the remotest periods there has been ever a
coming in of new organic forms, and an extinction of those which pre-existed on
the earth; some species having endured for a longer, others for a shorter, time;
while none have ever reappeared after once dying out. The law which has governed
the succession of species, whether we adopt or reject the theory of
transmutation, seems to be expressed in the verse of the poet:--
Natura il fece, e poi ruppe la stampa. Ariosto.
Nature made him, and then broke the die.
And this circumstance it is, which confers on fossils their highest value as
chronological tests, giving to each of them, in the eyes of the geologist, that
authority which belongs to contemporary medals in history.
The same can not be said of each peculiar variety of rock; for some of these, as
red marl and red sandstone, for example, may occur at once at the top, bottom,
and middle of the entire sedimentary series; exhibiting in each position so
perfect an identity of mineral aspect as to be undistinguishable. Such exact
repetitions, however, of the same mixtures of sediment have not often been
produced, at distant periods, in precisely the same parts of the globe; and even
where this has happened, we are seldom in any danger of confounding together the
monuments of remote eras, when we have studied their imbedded fossils and their
It was remarked that the same species of organic remains can not be traced
horizontally, or in the direction of the planes of stratifications for
indefinite distances. This might have been expected from analogy; for when we
inquire into the present distribution of living beings, we find that the
habitable surface of the sea and land may be divided into a considerable number
of distinct provinces, each peopled by a peculiar assemblage of animals and
plants. In the "Principles of Geology," I have endeavoured to point out the
extent and probable origin of these separate divisions; and it was shown that
climate is only one of many causes on which they depend, and that difference of
longitude as well as latitude is generally accompanied by a dissimilarity of
As different seas, therefore, and lakes are inhabited, at the same period, by
different aquatic animals and plants, and as the lands adjoining these may be
peopled by distinct terrestrial species, it follows that distinct fossils will
be imbedded in contemporaneous deposits. If it were otherwise-- if the same
species abounded in every climate, or in every part of the globe where, so far
as we can discover, a corresponding temperature and other conditions favourable
to their existence are found-- the identification of mineral masses of the same
age, by means of their included organic contents, would be a matter of still
Nevertheless, the extent of some single zoological provinces, especially those
of marine animals, is very great; and our geological researches have proved that
the same laws prevailed at remote periods; for the fossils are often identical
throughout wide spaces, and in detached deposits, consisting of rocks varying
entirely in their mineral nature.
The doctrine here laid down will be more readily understood, if we reflect on
what is now going on in the Mediterranean. That entire sea may be considered as
one zoological province; for although certain species of testacea and zoophytes
may be very local, and each region has probably some species peculiar to it,
still a considerable number are common to the whole Mediterranean. If,
therefore, at some future period, the bed of this inland sea should be converted
into land, the geologist might be enabled, by reference to organic remains, to
prove the contemporaneous origin of various mineral masses scattered over a
space equal in area to half of Europe.
Deposits, for example, are well known to be now in progress in this sea in the
deltas of the Po, Rhone, Nile, and other rivers, which differ as greatly from
each other in the nature of their sediment as does the composition of the
mountains which their drain. There are also other quarters of the Mediterranean,
as off the coast of Campania, or near the base of Etna, in Sicily, or in the
Grecian Archipelago, where another class of rocks is now forming; where showers
of volcanic ashes occasionally fall into the sea, and streams of lava overflow
its bottom; and where, in the intervals between volcanic eruptions, beds of sand
and clay are frequently derived from the waste of cliffs, or the turbid waters
of rivers. Limestones, moreover, such as the Italian travertins, are here and
there precipitated from the waters of mineral springs, some of which rise up
from the bottom of the sea. In all these detached formations, so diversified in
their lithological characters, the remains of the same shells, corals,
crustacea, and fish are becoming inclosed; or, at least, a sufficient number
must be common to the different localities to enable the zoologist to refer them
all to one contemporaneous assemblage of species.
There are, however, certain combinations of geographical circumstances which
cause distinct provinces of animals and plants to be separated from each other
by very narrow limits; and hence it must happen that strata will be sometimes
formed in contiguous regions, differing widely both in mineral contents and
organic remains. Thus, for example, the testacea, zoophytes, and fish of the Red
Sea are, as a group, extremely distinct from those inhabiting the adjoining
parts of the Mediterranean, although the two seas are separated only by the
narrow isthmus of Suez. Calcareous formations have accumulated on a great scale
in the Red Sea in modern times, and fossil shells of existing species are well
preserved therein; and we know that at the mouth of the Nile large deposits of
mud are amassed, including the remains of Mediterranean species. It follows,
therefore, that if at some future period the bed of the Red Sea should be laid
dry, the geologist might experience great difficulties in endeavouring to
ascertain the relative age of these formations, which, although dissimilar both
in organic and mineral characters, were of synchronous origin.
But, on the other hand, we must not forget that the north-western shores of the
Arabian Gulf, the plains of Egypt, and the Isthmus of Suez, are all parts of one
province of TERRESTRIAL species. Small streams, therefore, occasional land-
floods, and those winds which drift clouds of sand along the deserts, might
carry down into the Red Sea the same shells of fluviatile and land testacea
which the Nile is sweeping into its delta, together with some remains of
terrestrial plants and the bones of quadrupeds, whereby the groups of strata
before alluded to might, notwithstanding the discrepancy of their mineral
composition and MARINE organic fossils, be shown to have belonged to the same
Yet, while rivers may thus carry down the same fluviatile and terrestrial spoils
into two or more seas inhabited by different marine species, it will much more
frequently happen that the coexistence of terrestrial species of distinct
zoological and botanical provinces will be proved by the identity of the marine
beings which inhabited the intervening space. Thus, for example, the land
quadrupeds and shells of the valley of the Mississippi, of central America, and
of the West India islands differ very considerably, yet their remains are all
washed down by rivers flowing from these three zoological provinces into the
Gulf of Mexico.
In some parts of the globe, at the present period, the line of demarkation
between distinct provinces of animals and plants is not very strongly marked,
especially where the change is determined by temperature, as it is in seas
extending from the temperate to the tropical zone, or from the temperate to the
arctic regions. Here a gradual passage takes place from one set of species to
another. In like manner the geologist, in studying particular formations of
remote periods, has sometimes been able to trace the gradation from one ancient
province to another, by observing carefully the fossils of all the intermediate
places. His success in thus acquiring a knowledge of the zoological or botanical
geography of very distant eras has been mainly owing to this circumstance, that
the mineral character has no tendency to be affected by climate. A large river
may convey yellow or red mud into some part of the ocean, where it may be
dispersed by a current over an area several hundred leagues in length, so as to
pass from the tropics into the temperate zone. If the bottom of the sea be
afterwards upraised, the organic remains imbedded in such yellow or red strata
may indicate the different animals or plants which once inhabited at the same
time the temperate and equatorial regions.
It may be true, as a general rule, that groups of the same species of animals
and plants may extend over wider areas than deposits of homogeneous composition;
and if so, palaeontological characters will be of more importance in geological
classification than the test of mineral composition; but it is idle to discuss
the relative value of these tests, as the aid of both is indispensable, and it
fortunately happens, that where the one criterion fails, we can often avail
ourselves of the other.
TEST BY INCLUDED FRAGMENTS OF OLDER ROCKS.
It was stated, that proof may sometimes be obtained of the relative date of two
formations by fragments of an older rock being included in a newer one. This
evidence may sometimes be of great use, where a geologist is at a loss to
determine the relative age of two formations from want of clear sections
exhibiting their true order of position, or because the strata of each group are
vertical. In such cases we sometimes discover that the more modern rock has been
in part derived from the degradation of the older. Thus, for example, we may
find chalk in one part of a country, and in another strata of clay, sand, and
pebbles. If some of these pebbles consist of that peculiar flint, of which
layers more or less continuous are characteristic of the chalk, and which
include fossil shells, sponges, and foraminifera of cretaceous species, we may
confidently infer that the chalk was the oldest of the two formations.
The number of groups into which the fossiliferous strata may be separated are
more or less numerous, according to the views of classification which different
geologists entertain; but when we have adopted a certain system of arrangement,
we immediately find that a few only of the entire series of groups occur one
upon the other in any single section or district.
(FIGURE 84. Seven fossiliferous groups.)
The thinning out of individual strata was before described (Chapter 2). But let
the diagram (Figure 84) represent seven fossiliferous groups, instead of as many
strata. It will then be seen that in the middle all the superimposed formations
are present; but in consequence of some of them thinning out, No. 2 and No. 5
are absent at one extremity of the section, and No. 4 at the other.
(FIGURE 85. Section South of Bristol (A.C. Ramsay.)
Length of section 4 miles.
a-b. Level of the sea.
1. Inferior Oolite.
3. New Red Sandstone.
4. Dolomitic or magnesian conglomerate.
5. Upper coal-measures (shales, etc.)
6. Pennant rock (sandstone.)
7. Lower coal-measures (shales, etc.)
8. Carboniferous or mountain limestone.
9. Old Red Sandstone.)
In another diagram (Figure 85), a real section of the geological formations in
the neighbourhood of Bristol and the Mendip Hills is presented to the reader, as
laid down on a true scale by Professor Ramsay, where the newer groups 1, 2, 3, 4
rest unconformably on the formations 5, 6, 7 and 8. At the southern end of the
line of section we meet with the beds No. 3 (the New Red Sandstone) resting
immediately on Nos. 7 and 8, while farther north as at Dundry Hill in
Somersetshire, we behold eight groups superimposed one upon the other,
comprising all the strata from the inferior Oolite, No. 1, to the coal and
carboniferous limestone. The limited horizontal extension of the groups 1 and 2
is owing to denudation, as these formations end abruptly, and have left outlying
patches to attest the fact of their having originally covered a much wider area.
In order, therefore, to establish a chronological succession of fossiliferous
groups, a geologist must begin with a single section in which several sets of
strata lie one upon the other. He must then trace these formations, by attention
to their mineral character and fossils, continuously, as far as possible, from
the starting-point. As often as he meets with new groups, he must ascertain by
superposition their age relatively to those first examined, and thus learn how
to intercalate them in a tabular arrangement of the whole.
By this means the German, French, and English geologists have determined the
succession of strata throughout a great part of Europe, and have adopted pretty
generally the following groups, almost all of which have their representatives
in the British Islands.
ABRIDGED GENERAL TABLE OF FOSSILIFEROUS STRATA.
1. RECENT.-- POST-TERTIARY.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
2. POST-PLIOCENE.-- POST-TERTIARY.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
3. NEWER-PLIOCENE.-- PLIOCENE.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
4. OLDER PLIOCENE.-- PLIOCENE.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
5. UPPER MIOCENE.-- MIOCENE.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
6. LOWER MIOCENE.-- MIOCENE.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
7. UPPER EOCENE.-- EOCENE.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
8. MIDDLE EOCENE.-- EOCENE.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
9. LOWER EOCENE.-- EOCENE.-- TERTIARY OR CAINOZOIC.-- NEOZOIC.
10. MAESTRICHT BEDS.-- CRETACEOUS.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
11. WHITE CHALK.-- CRETACEOUS.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
12. CHLORITIC SERIES.-- CRETACEOUS.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
13. GAULT.-- CRETACEOUS.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
14. NEOCOMIAN.-- CRETACEOUS.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
15. WEALDEN.-- CRETACEOUS.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
16. PURBECK BEDS.-- JURASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
17. PORTLAND STONE.-- JURASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
18. KIMMERIDGE CLAY.-- JURASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
19. CORAL RAG.-- JURASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
20. OXFORD CLAY.-- JURASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
21. GREAT or BATH OOLITE.-- JURASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
22. INFERIOR OOLITE.-- JURASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
23. LIAS.-- JURASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
24. UPPER TRIAS.-- TRIASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
25. MIDDLE TRIAS.-- TRIASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
26. LOWER TRIAS.-- TRIASSIC.-- SECONDARY OR MESOZOIC.-- NEOZOIC.
27. PERMIAN.-- PERMIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
28. COAL-MEASURES.-- CARBONIFEROUS.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
29. CARBONIFEROUS LIMESTONE.-- CARBONIFEROUS.-- -- PRIMARY OR PALAEOZOIC.--
30. UPPER DEVONIAN.-- DEVONIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
31. MIDDLE DEVONIAN.-- DEVONIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
32. LOWER DEVONIAN.-- DEVONIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
33. UPPER SILURIAN.-- SILURIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
34. LOWER SILURIAN.-- SILURIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
35. UPPER CAMBRIAN.-- CAMBRIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
36. LOWER CAMBRIAN.-- CAMBRIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
37. UPPER LAURENTIAN.-- LAURENTIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
38. LOWER LAURENTIAN.-- LAURENTIAN.-- PRIMARY OR PALAEOZOIC.-- PALAEOZOIC.
TABULAR VIEW OF THE FOSSILIFEROUS STRATA,
SHOWING THE ORDER OF SUPERPOSITION OR CHRONOLOGICAL SUCCESSION OF THE PRINCIPAL
GROUPS DESCRIBED IN THIS WORK (CITING EXAMPLES).
1. RECENT. Shells and mammalia, all of living species.
Clyde marine strata, with canoes (Chapter 10.)
Danish kitchen middens (Chapter 10.)
Lacustrine mud, with remains of Swiss lake-dwellings (Chapter 10.)
Marine strata inclosing Temple of Serapis, at Puzzuoli (Chapter 10.)
2. POST-PLIOCENE. Shells, recent mammalia in part extinct.
Loam of Brixham cave, with flint implements and bones of extinct and living
quadrupeds. (Chapter 10.)
Drift near Salisbury, with bones of mammoth, Spermophilus, and stone implements.
Glacial drift of Scotland, with marine shells and remains of mammoth. (Chapter
Erratics of Pagham and Selsey Bill. (Chapter 11.)
Glacial drift of Wales, with marine fossil shells, about 1400 feet high, on Moel
Tryfaen. (Chapter 11.)
Dordogne caves of the reindeer period. (Chapter 10.)
Older valley-gravels of Amiens, with flint implements and bones of extinct
mammalia. (Chapter 10.)
Loess of Rhine. (Chapter 10.)
Ancient Nile-mud forming river-terraces. (Chapter 10.)
Loam and breccia of Liege caverns, with human remains. (Chapter 10.)
Australian cave breccias, with bones of extinct marsupials. (Chapter 10.)
Glacial drift of Northern Europe. (Chapters 11 and 12.)
TERTIARY OR CAINOZOIC.
3. NEWER PLIOCENE. The shells almost all of living species.
Bridlington beds, marine Arctic fauna. (Chapter 13.)
Glacial boulder formation of Norfolk cliffs. (Chapter 13.)
Forest-bed of Norfolk cliffs, with bones of Elephas meridionalis, etc. (Chapter
Chillesford and Aldeby beds, with marine shells, chiefly Arctic. (Chapter 13.)
Norwich Crag. (Chapter 13.)
Eastern base of Mount Etna, with marine shells. (Chapter 13.)
Sicilian calcareous and tufaceous strata. (Chapter 13.)
Lacustrine strata of Upper Val d'Arno. (Chapter 13.)
Madeira leaf-bed and land-shells. (Chapter 29.)
4. OLDER PLIOCENE. Extinct species of shells forming a large minority.
Red crag of Suffolk, marine shells, some of northern forms. (Chapter 13.)
White or coralline crag of Suffolk. (Chapter 13.)
Antwerp crag. (Chapter 13.)
Subapennine marls and sands. (Chapter 13.)
5. UPPER MIOCENE. Majority of the shells extinct.
faluns of Touraine (Chapter 14.)
faluns, proper, of Bordeaux. (Chapter 14.)
Fresh-water strata of Gers. (Chapter 14.)
Swiss Oeningen beds, rich in plants and insects. (Chapter 14.)
Marine Molasse, Switzerland. (Chapter 14.)
Bolderberg beds of Belgium. (Chapter 14.)
Vienna basin. (Chapter 14.)
Beds of the Superga, near Turin. (Chapter 14.)
Deposit at Pikerme, near Athens. (Chapter 14.)
Strata of the Siwalik hills, India. (Chapter 14.)
Marine strata of the Atlantic border in the United States. (Chapter 14.)
Volcanic tuff and limestone of Madeira, the Canaries, and the Azores. (Chapter
6. LOWER MIOCENE. Nearly all the shells extinct.
Hempstead beds, marine and fresh-water strata. (Chapter 15.)
Lignites and clays of Bovey Tracey. (Chapter 15.)
Isle of Mull leaf-bed, volcanic tuff. (Chapter 15.)
Calcaire de la Beauce, etc. (Chapter 15.)
Gres de Fontainebleau. (Chapter 15.)
Lacustrine strata of the Limagne d'Auvergne, and the Cantal. (Chapter 15.)
Mayence basin. (Chapter 15.)
Radaboj beds of Croatia. (Chapter 15.)
Brown coal of Germany. (Chapter 15.)
Lower Molasse of Switzerland, fresh-water and brackish. (Chapter 15.)
Rupelmonde, Kleynspawen, and Tongrian beds of Belgium. (Chapter 15.)
Nebraska beds, United States. (Chapter 15.)
Lower Miocene beds of Italy. (Chapter 15.)
Miocene flora of North Greenland. (Chapter 15.)
7. UPPER EOCENE.
Bembridge fluvio-marine strata. (Chapter 16.)
Osborne or St. Helen's series. (Chapter 16.)
Headon series, with marine and fresh-water shells. (Chapter 16.)
Barton sands and clays (Chapter 16.)
Gypsum of Montmartre, fresh-water with Palaeotherium. (Chapter 16.)
Calcaire silicieux, or Travertin inferieur. (Chapter 16.)
Gres de Beauchamp, or Sables moyens. (Chapter 16.)
8. MIDDLE EOCENE.
Bracklesham beds and Bagshot sands. (Chapter 16.)
White clays of Alum Bay and Bournemouth. (Chapter 16.)
Calcaire grossier, miliolitic limestone. (Chapter 16.)
Soissonnais sands, or Lits coquilliers, with Nummulites planulata. (Chapter 16.)
Claiborne beds of the United States, with Orbitoides and Zeuglodon. (Chapter
9. LOWER EOCENE.
Nummulitic formation of Europe, Asia, etc. (Chapter 16.)
London Clay proper. (Chapter 16.)
Woolwich and Reading series, fluvio-marine. (Chapter 16.)
Thanet sands. (Chapter 16.)
Argile de Londres, near Dunkirk. (Chapter 16.)
Argile plastique. (Chapter 16.)
Sables de Bracheux. (Chapter 16.)
SECONDARY OR MESOZOIC.
10. UPPER CRETACEOUS.
Upper white chalk, with flints. (Chapter 17.)
Lower white chalk, without flints. (Chapter 17.)
Chalk marl. (Chapter 17.)
Chloritic series (or Upper Greensand), fire-stone of Surrey. (Chapter 17.)
Gault. (Chapter 17.)
Blackdown beds. (Chapter 17.)
Maestricht beds and Faxoe chalk. (Chapter 17.)
Pisolitic limestone of France. (Chapter 17.)
White chalk of France, Sweden, and Russia. (Chapter 17.)
Planer-kalk of Saxony. (Chapter 17.)
Sands and clays of Aix-la-Chapelle. (Chapter 17.)
Hippurite limestone of South of France. (Chapter 17.)
New Jersey, U.S., sands and marls. (Chapter 17.)
11. LOWER CRETACEOUS OR NEOCOMIAN.
Sands of Folkestone, Sandgate, and Hythe. (Chapter 18.)
Atherfield clay, with Perna mulleti. (Chapter 18.)
Punfield marine beds, with Vicarya lujana. (Chapter 18.)
Speeton clay of Flamborough Head and Tealby. (Chapter 18.)
Weald clay of Surrey, Kent, and Sussex, fresh-water, with Cypris. (Chapter 18.)
Neocomian of Neufchatel, and Hils conglomerate of North Germany. (Chapter 18.)
Wealden beds of Hanover. (Chapter 18.)
12. UPPER OOLITE.
Upper Purbeck beds, fresh-water. (Chapter 19.)
Middle Purbeck, with numerous marsupial quadrupeds, etc. (Chapter 19.)
Lower Purbeck, fresh-water, with intercalated dirt-bed. (Chapter 19.)
Portland stone and sand. (Chapter 19.)
Kimmeridge clay. (Chapter 19.)
Marnes a gryphees virgules of Argonne. (Chapter 19.)
Lithographic-stone of Solenhofen, with Archaeopteryx. (Chapter 19.)
13. MIDDLE OOLITE.
Coral rag of Berkshire, Wilts, and Yorkshire. (Chapter 19.)
Oxford clay, with belemnites and Ammonite. (Chapter 19.)
Kelloway rock of Wilts and Yorkshire. (Chapter 19.)
Nerinaean limestone of the Jura.
14. LOWER OOLITE.
Cornbrash and forest marble. (Chapter 19.)
Great or Bath oolite of Bradford. (Chapter 19.)
Stonesfield slate, with marsupials and Araucaria. (Chapter 19.)
Fuller's earth of Bath. (Chapter 19.)
Inferior oolite. (Chapter 19.)
Upper Lias, argillaceous, with Ammonites striatulus. (Chapter 20.)
Shale and limestone, with Ammonites bifrons. (Chapter 20.)
Middle Lias or Marlstone series, with zones containing characteristic Ammonites.
Lower Lias, also with zones characterised by peculiar Ammonites. (Chapter 20.)
16. UPPER TRIAS.
Rhaetic, Penarth or Avicula contorta beds (beds of passage). (Chapter 21.)
Keuper or Upper New Red sandstone, etc. (Chapter 21.)
Red shales of Cheshire and Lancashire, with rock-salt. (Chapter 21.)
Dolomite conglomerate of Bristol (Chapter 21.)
Keuper beds of Germany. (Chapter 21.)
St. Cassian or Hallstadt beds, with rich marine fauna. (Chapter 21.)
Coal-field of Richmond, Virginia. (Chapter 21.)
Chatham coal-field, North Carolina. (Chapter 21.)
17. MIDDLE TRIAS.
Muschelkalk of Germany. (Chapter 21.)
18. LOWER TRIAS.
Bunter or Lower New Red sandstone of Lancashire and Cheshire. (Chapter 21.)
Bunter-sandstein of Germany. (Chapter 21.)
Red sandstone of Connecticut Valley, with footprints of birds and reptiles.
PRIMARY OR PALAEOZOIC.
Upper Permian of St. Bees' Head, Cumberland. (Chapter 22.)
Middle Permian, magnesian limestone, and marl-slate of Durham and Yorkshire,
with Protosaurus. (Chapter 22.)
Lower Permian sandstones and breccias of Penrith and Dumfriesshire,
intercalated. (Chapter 22.)
Dark-coloured shales of Thuringia. (Chapter 22.)
Zechstein or Dolomitic limestone. (Chapter 22.)
Mergel-schiefer or Kupfer-schiefer. (Chapter 22.)
Rothliegendes of Thuringia, with Psaronius. (Chapter 22.)
Magnesian limestones, etc., of Russia. (Chapter 22.)
20. UPPER CARBONIFEROUS.
Coal-measures of South Wales, with underclays inclosing Stigmaria. (Chapter 23.)
Coal-measures of north and central England. (Chapter 23.)
Millstone grit. (Chapter 23.)
Yoredale series of Yorkshire. (Chapter 23.)
Coal-field of Kilkenny with Labyrinthodont. (Chapter 23.)
Coal-field of Saarbruck, with Archegosaurus. (Chapter 23.)
Carboniferous strata of South Joggins, Nova Scotia. (Chapter 23.)
Pennsylvania coal-field. (Chapter 23.)
21. LOWER CARBONIFEROUS.
Mountain limestone of Wales and South of England. (Chapter 24.)
Same in Ireland. (Chapter 24.)
Carboniferous limestone of Scotland alternating with coal-bearing sandstones.
Erect trees in volcanic ash in the Island of Arran. (Chapter 30.)
Mountain limestone of Belgium. (Chapter 24.)
DEVONIAN OR OLD RED SANDSTONE.
22. UPPER DEVONIAN.
Yellow sandstone of Dura Den, with Holoptychius, etc. (Chapter 25.); and of
Ireland with Anodon Jukesii. (Chapter 25.)
Sandstones of Forfarshire and Perthshire, with Holoptychius, etc. (Chapter 25.)
Pilton group of North Devon. (Chapter 25.)
Petherwyn group of Cornwall, with Clymenia and Cypridina. (Chapter 25.)
Clymenien-kalk and Cypridinen-schiefer of Germany. (Chapter 25.)
23. MIDDLE DEVONIAN.
Bituminous schists of Gamrie, Caithness, etc., with numerous fish. (Chapter 25.)
Ilfracombe beds with peculiar trilobites and corals. (Chapter 25.)
Limestones of Torquay, with broad-winged Spirifers. (Chapter 25.)
FOREIGN. (Chapter 25.)
Eifel limestone, with underlying schists containing Calceola. (Chapter 25.)
Devonian strata of Russia. (Chapter 25.)
24. LOWER DEVONIAN.
Arbroath paving-stones, with Cephalaspis and Pterygotus. (Chapter 25.)
Lower sandstones of Forfarshire, with Pterygotus. (Chapter 25.)
Sandstones and slates of the Foreland and Linton. (Chapter 25.)
Oriskany sandstone of Western Canada and New York. (Chapter 25.)
Sandstones of Gaspe, with Cephalaspis. (Chapter 25.)
25. UPPER SILURIAN.
Upper Ludlow formation, Downton sandstone, with bone-bed. (Chapter 26.)
Lower Ludlow formation, with oldest known fish remains. (Chapter 26.)
Wenlock limestone and shale. (Chapter 26.)
Woolhope limestone and grit. (Chapter 26.)
Tarannon shales. (Chapter 26.)
Beds of passage between Upper and Lower Silurian:
Upper Llandovery, or May-hill sandstone, with Pentamerus oblongus, etc. (Chapter
Lower Llandovery slates. (Chapter 26.)
Niagara limestone, with Calymene, Homalonotus, etc. (Chapter 26.)
Clinton group of America, with Pentamerus oblongus, etc. (Chapter 26.)
Silurian strata of Russia, with Pentamerus. (Chapter 26.)
26. LOWER SILURIAN.
Bala and Caradoc beds. (Chapter 26.)
Llandeilo flags. (Chapter 26.)
Arenig or Stiper-stones group (Lower Llandeilo of Murchison.) (Chapter 26.)
Ungulite or Obolus grit of Russia. (Chapter 26.)
Trenton limestone, and other Lower Silurian groups of North America. (Chapter
Lower Silurian of Sweden. (Chapter 26.)
27. UPPER CAMBRIAN.
Tremadoc slates. (Chapter 27.)
Lingula flags, with Lingula Davisii. (Chapter 27.)
"Primordial" zone of Bohemia in part, with trilobites of the genera Paradoxides,
etc. (Chapter 27.)
Alum schists of Sweden and Norway. (Chapter 27.)
Potsdam sandstone, with Dikelocephalus and Obolella. (Chapter 27.)
28. LOWER CAMBRIAN.
Menevian beds of Wales, with Paradoxides Davidis, etc. (Chapter 27.)
Longmynd group, comprising the Harlech grits and Llanberis slates. (Chapter 27.)
Lower portion of Barrande's "Primordial" zone in Bohemia. (Chapter 27.)
Fucoid sandstones of Sweden. (Chapter 27.)
Huronian series of Canada? (Chapter 27.)
29. UPPER LAURENTIAN.
Fundamental gneiss of the Hebrides? (Chapter 27.)
Hypersthene rocks of Skye? (Chapter 27.)
Labradorite series north of the river St. Lawrence in Canada. (Chapter 27.)
Adirondack mountains of New York. (Chapter 27.)
30. LOWER LAURENTIAN.
Beds of gneiss and quartzite, with interstratified limestones, in one of which,
1000 feet thick, occurs a foraminifer, Eozoon Canadense, the oldest known
fossil. (Chapter 27.)
CLASSIFICATION OF TERTIARY FORMATIONS.
Order of Succession of Sedimentary Formations.
Frequent Unconformability of Strata.
Imperfection of the Record.
Defectiveness of the Monuments greater in Proportion to their Antiquity.
Reasons for studying the newer Groups first.
Nomenclature of Formations.
Detached Tertiary Formations scattered over Europe.
Value of the Shell-bearing Mollusca in Classification.
Classification of Tertiary Strata.
Eocene, Miocene, and Pliocene Terms explained.
By reference to the tables given at the end of the last chapter the reader will
see that when the fossiliferous rocks are arranged chronologically, we have
first to consider the Post-tertiary and then the Tertiary or Cainozoic
formations, and afterwards to pass on to those of older date.
ORDER OF SUPERPOSITION.
(FIGURE 86. Section through Primary (left), Secondary, Tertiary and Post-
tertiary (right) Strata.
The diagram (Figure 86.) will show the order of superposition of these deposits,
assuming them all to be visible in one continuous section. In nature, as before
hinted (Chapter 6), we have never an opportunity of seeing the whole of them so
displayed in a single region; first, because sedimentary deposition is confined,
during any one geological period, to limited areas; and secondly, because
strata, after they have been formed, are liable to be utterly annihilated over
wide areas by denudation. But wherever certain members of the series are
present, they overlie one another in the order indicated in the diagram, though
not always in the exact manner there represented, because some of them repose
occasionally in unconformable stratification on others. This mode of
superposition has been already explained (Chapters 5 and 7), where I pointed out
that the discordance which implies a considerable lapse of time between two
formations in juxtaposition is almost invariably accompanied by a great
dissimilarity in the species of organic remains.
FREQUENT UNCONFORMABILITY OF STRATA.
Where the widest gaps appear in the sequence of the fossil forms, as between the
Permian and Triassic rocks, or between the Cretaceous and Eocene, examples of
such unconformability are very frequent. But they are also met with in some part
or other of the world at the junction of almost all the other principal
formations, and sometimes the subordinate divisions of any one of the leading
groups may be found lying unconformably on another subordinate member of the
same-- the Upper, for example, on the Lower Silurian, or the superior division
of the Old Red Sandstone on a lower member of the same, and so forth. Instances
of such irregularities in the mode of succession of the strata are the more
intelligible the more we extend our survey of the fossiliferous formations, for
we are continually bringing to light deposits of intermediate date, which have
to be intercalated between those previously known, and which reveal to us a long
series of events, of which antecedently to such discoveries we had no knowledge.
But while unconformability invariably bears testimony to a lapse of
unrepresented time, the conformability of two sets of strata in contact by no
means implies that the newer formation immediately succeeded the older one. It
simply implies that the ancient rocks were subjected to no movements of such a
nature as to tilt, bend, or break them before the more modern formation was
superimposed. It does not show that the earth's crust was motionless in the
region in question, for there may have been a gradual sinking or rising,
extending uniformly over a large surface, and yet, during such movement, the
stratified rocks may have retained their original horizontality of position.
There may have been a conversion of a wide area from sea into land and from land
into sea, and during these changes of level some strata may have been slowly
removed by aqueous action, and after this new strata may be superimposed,
differing perhaps in date by thousands of years or centuries, and yet resting
conformably on the older set. There may even be a blending of the materials
constituting the older deposit with those of the newer, so as to give rise to a
passage in the mineral character of the one rock into the other as if there had
been no break or interruption in the depositing process.
IMPERFECTION OF THE RECORD.
Although by the frequent discovery of new sets of intermediate strata the
transition from one type of organic remains to another is becoming less and less
abrupt, yet the entire series of records appears to the geologists now living
far more fragmentary and defective than it seemed to their predecessors half a
century ago. The earlier inquirers, as often as they encountered a break in the
regular sequence of formations, connected it theoretically with a sudden and
violent catastrophe, which had put an end to the regular course of events that
had been going on uninterruptedly for ages, annihilating at the same time all or
nearly all the organic beings which had previously flourished, after which,
order being re-established, a new series of events was initiated. In proportion
as our faith in these views grows weaker, and the phenomena of the organic or
inorganic world presented to us by geology seem explicable on the hypothesis of
gradual and insensible changes, varied only by occasional convulsions, on a
scale comparable to that witnessed in historical times; and in proportion as it
is thought possible that former fluctuations in the organic world may be due to
the indefinite modifiability of species without the necessity of assuming new
and independent acts of creation, the number and magnitude of the gaps which
still remain, or the extreme imperfection of the record, become more and more
striking, and what we possess of the ancient annals of the earth's history
appears as nothing when contrasted with that which has been lost.
When we examine a large area such as Europe, the average as well as the extreme
height above the sea attained by the older formations is usually found to exceed
that reached by the more modern ones, the primary or palaeozoic rising higher
than the secondary, and these in their turn than the tertiary; while in
reference to the three divisions of the tertiary, the lowest or Eocene group
attains a higher summit-level than the Miocene, and these again a greater height
than the Pliocene formations. Lastly, the post-tertiary deposits, such, at
least, as are of marine origin, are most commonly restricted to much more
moderate elevations above the sea-level than the tertiary strata.
It is also observed that strata, in proportion as they are of newer date, bear
the nearest resemblance in mineral character to those which are now in the
progress of formation in seas or lakes, the newest of all consisting principally
of soft mud or loose sand, in some places full of shells, corals, or other
organic bodies, animal or vegetable, in others wholly devoid of such remains.
The farther we recede from the present time, and the higher the antiquity of the
formations which we examine, the greater are the changes which the sedimentary
deposits have undergone. Time, as I have explained in Chapters 5, 6, and 7, has
multiplied the effects of condensation by pressure and cementation, and the
modification produced by heat, fracture, contortion, upheaval, and denudation.
The organic remains also have sometimes been obliterated entirely, or the
mineral matter of which they were composed has been removed and replaced by
WHY NEWER GROUPS SHOULD BE STUDIED FIRST.
We likewise observe that the older the rocks the more widely do their organic
remains depart from the types of the living creation. First, we find in the
newer tertiary rocks a few species which no longer exist, mixed with many living
ones, and then, as we go farther back, many genera and families at present
unknown make their appearance, until we come to strata in which the fossil
relics of existing species are nowhere to be detected, except a few of the
lowest forms of invertebrate, while some orders of animals and plants wholly
unrepresented in the living world begin to be conspicuous.
When we study, therefore, the geological records of the earth and its
inhabitants, we find, as in human history, the defectiveness and obscurity of
the monuments always increasing the remoter the era to which we refer, and the
difficulty of determining the true chronological relations of rocks is more and
more enhanced, especially when we are comparing those which were formed
simultaneously in very distant regions of the globe. Hence we advance with
securer steps when we begin with the study of the geological records of later
times, proceeding from the newer to the older, or from the more to the less
In thus inverting what might at first seem to be the more natural order of
historical research, we must bear in mind that each of the periods above
enumerated, even the shortest, such as the Post-tertiary, or the Pliocene,
Miocene, or Eocene, embrace a succession of events of vast extent, so that to
give a satisfactory account of what we already know of any one of them would
require many volumes. When, therefore, we approach one of the newer groups
before endeavouring to decipher the monuments of an older one, it is like
endeavouring to master the history of our own country and that of some
contemporary nations, before we enter upon Roman History, or like investigating
the annals of Ancient Italy and Greece before we approach those of Egypt and
The origin of the terms Primary and Secondary, and the synonymous terms
Palaeozoic, and Mesozoic, were explained in Chapter 8.
The Tertiary or Cainozoic strata (see Chapter 8) were so called because they
were all posterior in date to the Secondary series, of which last the Chalk of
Cretaceous, No. 9, Figure 86, constitutes the newest group. The whole of them
were at first confounded with the superficial alluviums of Europe; and it was
long before their real extent and thickness, and the various ages to which they
belong, were fully recognised. They were observed to occur in patches, some of
fresh-water, others of marine origin, their geographical area being usually
small as compared to the secondary formations, and their position often
suggesting the idea of their having been deposited in different bays, lakes,
estuaries, or inland seas, after a large portion of the space now occupied by
Europe had already been converted into dry land.
The first deposits of this class, of which the characters were accurately
determined, were those occurring in the neighbourhood of Paris, described in
1810 by MM. Cuvier and Brongniart. They were ascertained to consist of
successive sets of strata, some of marine, others of fresh-water origin, lying
one upon the other. The fossil shells and corals were perceived to be almost all
of unknown species, and to have in general a near affinity to those now
inhabiting warmer seas. The bones and skeletons of land animals, some of them of
large size, and belonging to more than forty distinct species, were examined by
Cuvier, and declared by him not to agree specifically, nor most of them even
generically, with any hitherto observed in the living creation.
Strata were soon afterwards brought to light in the vicinity of London, and in
Hampshire, which, although dissimilar in mineral composition, were justly
inferred by Mr. T. Webster to be of the same age as those of Paris, because the
greater number of the fossil shells were specifically identical. For the same
reason, rocks found on the Gironde, in the South of France, and at certain
points in the North of Italy, were suspected to be of contemporaneous origin.
Another important discovery was soon afterwards made by Brocchi in Italy, who
investigated the argillaceous and sandy deposits, replete with shells, which
form a low range of hills, flanking the Apennines on both sides, from the plains
of the Po to Calabria. These lower hills were called by him the Subapennines,
and were formed of strata chiefly marine, and newer than those of Paris and
Another tertiary group occurring in the neighbourhood of Bordeaux and Dax, in
the South of France, was examined by M. de Basterot in 1825, who described and
figured several hundred species of shells, which differed for the most part both
from the Parisian series and those of the Subapennine hills. It was soon,
therefore, suspected that this fauna might belong to a period intermediate
between that of the Parisian and Subapennine strata, and it was not long before
the evidence of superposition was brought to bear in support of this opinion;
for other strata, contemporaneous with those of Bordeaux, were observed in one
district (the Valley of the Loire), to overlie the Parisian formation, and in
another (in Piedmont) to underlie the Subapennine beds. The first example of
these was pointed out in 1829 by M. Desnoyers, who ascertained that the sand and
marl of marine origin called faluns, near Tours, in the basin of the Loire, full
of sea-shells and corals, rested upon a lacustrine formation, which constitutes
the uppermost subdivision of the Parisian group, extending continuously
throughout a great table-land intervening between the basin of the Seine and
that of the Loire. The other example occurs in Italy, where strata containing
many fossils similar to those of Bordeaux were observed by Bonelli and others in
the environs of Turin, subjacent to strata belonging to the Subapennine group of
VALUE OF TESTACEAN FOSSILS IN CLASSIFICATION.
It will be observed that in the foregoing allusions to organic remains, the
testacea or the shell-bearing mollusca are selected as the most useful and
convenient class for the purposes of general classification. In the first place,
they are more universally distributed through strata of every age than any other
organic bodies. Those families of fossils which are of rare and casual
occurrence are absolutely of no avail in establishing a chronological
arrangement. If we have plants alone in one group of strata and the bones of
mammalia in another, we can draw no conclusion respecting the affinity or
discordance of the organic beings of the two epochs compared; and the same may
be said if we have plants and vertebrated animals in one series and only shells
in another. Although corals are more abundant, in a fossil state, than plants,
reptiles, or fish, they are still rare when contrasted with shells, because they
are more dependent for their well-being on the constant clearness of the water,
and are, therefore, less likely to be included in rocks which endure in
consequence of their thickness and the copiousness of sediment which prevailed
when they originated. The utility of the testacea is, moreover, enhanced by the
circumstance that some forms are proper to the sea, others to the land, and
others to fresh water. Rivers scarcely ever fail to carry down into their deltas
some land-shells, together with species which are at once fluviatile and
lacustrine. By this means we learn what terrestrial, fresh-water, and marine
species coexisted at particular eras of the past: and having thus identified
strata formed in seas with others which originated contemporaneously in inland
lakes, we are then enabled to advance a step farther, and show that certain
quadrupeds or aquatic plants, found fossil in lacustrine formations, inhabited
the globe at the same period when certain fish, reptiles, and zoophytes lived in
Among other characters of the molluscous animals, which render them extremely
valuable in settling chronological questions in geology, may be mentioned,
first, the wide geographical range of many species; and, secondly, what is
probably a consequence of the former, the great duration of species in this
class, for they appear to have surpassed in longevity the greater number of the
mammalia and fish. Had each species inhabited a very limited space, it could
never, when imbedded in strata, have enabled the geologist to identify deposits
at distant points; or had they each lasted but for a brief period, they could
have thrown no light on the connection of rocks placed far from each other in
the chronological, or, as it is often termed, vertical series.
CLASSIFICATION OF TERTIARY STRATA.
Many authors have divided the European Tertiary strata into three groups--
lower, middle, and upper; the lower comprising the oldest formations of Paris
and London before mentioned; the middle those of Bordeaux and Touraine; and the
upper all those newer than the middle group.
In the first edition of the Principles of Geology, I divided the whole of the
Tertiary formations into four groups, characterised by the percentage of recent
shells which they contained. The lower tertiary strata of London and Paris were
thought by M. Deshayes to contain only 3 1/2 per cent of recent species, and
were termed Eocene. The middle tertiary of the Loire and Gironde had, according
to the specific determinations of the same conchologist, 17 per cent, and formed
the Miocene division. The Subapennine beds contained 35 to 50 per cent, and were
termed Older Pliocene, while still more recent beds in Sicily, which had from 90
to 95 per cent of species identical with those now living, were called Newer
Pliocene. The first of the above terms, Eocene, is derived from eos, dawn, and
cainos, recent, because the fossil shells of this period contain an extremely
small proportion of living species, which may be looked upon as indicating the
dawn of the existing state of the testaceous fauna, no recent species having
been detected in the older or secondary rocks.
The term Miocene (from meion, less, and cainos, recent) is intended to express a
minor proportion of recent species (of testacea), the term Pliocene (from
pleion, more, and cainos, recent) a comparative plurality of the same. It may
assist the memory of students to remind them, that the MI-ocene contain a MI-nor
proportion, and PL-iocene a comparative PL-urality of recent species; and that
the greater number of recent species always implies the more modern origin of
It has sometimes been objected to this nomenclature that certain species of
infusoria found in the chalk are still existing, and, on the other hand, the
Miocene and Older Pliocene deposits often contain the remains of mammalia,
reptiles, and fish, exclusively of extinct species. But the reader must bear in
mind that the terms Eocene, Miocene, and Pliocene were originally invented with
reference purely to conchological data, and in that sense have always been and
are still used by me.
Since the year 1830 the number of known shells, both recent and fossil, has
largely increased, and their identification has been more accurately determined.
Hence some modifications have been required in the classifications founded on
less perfect materials. The Eocene, Miocene, and Pliocene periods have been made
to comprehend certain sets of strata of which the fossils do not always conform
strictly in the proportion of recent to extinct species with the definitions
first given by me, or which are implied in the etymology of those terms.
RECENT AND POST-PLIOCENE PERIODS.
Recent and Post-pliocene Periods.
Formations of the Recent Period.
Modern littoral Deposits containing Works of Art near Naples.
Danish Peat and Shell-mounds.
Periods of Stone, Bronze, and Iron.
Coexistence of Man with extinct Mammalia.
Reindeer Period of South of France.
Alluvial Deposits of Paleolithic Age.
Higher and Lower-level Valley-gravels.
Loess or Inundation-mud of the Nile, Rhine, etc.
Origin of Caverns.
Remains of Man and extinct Quadrupeds in Cavern Deposits.
Cave of Kirkdale.
Geographical Relationship of the Provinces of living Vertebrata and those of
extinct Post-pliocene Species.
Extinct struthious Birds of New Zealand.
Climate of the Post-pliocene Period.
Comparative Longevity of Species in the Mammalia and Testacea.
Teeth of Recent and Post-pliocene Mammalia.
We have seen in the last chapter that the uppermost or newest strata are called
Post-tertiary, as being more modern than the Tertiary. It will also be observed
that the Post-tertiary formations are divided into two subordinate groups: the
Recent, and Post-pliocene. In the former, or the Recent, the mammalia as well as
the shells are identical with species now living: whereas in the Post-pliocene,
the shells being all of living forms, a part, and often a considerable part, of
the mammalia belonged to extinct species. To this nomenclature it may be
objected that the term Post-pliocene should in strictness include all geological
monuments posterior in date to the Pliocene; but when I have occasion to speak
of the whole collectively, I shall call them Post-tertiary, and reserve the term
Post-pliocene for the older Post-tertiary formations, while the Upper or newer
ones will be called "Recent."
Cases will occur where it may be scarcely possible to draw the boundary line
between the Recent and Post-pliocene deposits; and we must expect these
difficulties to increase rather than diminish with every advance in our
knowledge, and in proportion as gaps are filled up in the series of records.
It was stated in the sixth chapter, when I treated of denudation, that the dry
land, or that part of the earth's surface which is not covered by the waters of
lakes or seas, is generally wasting away by the incessant action of rain and
rivers, and in some cases by the undermining and removing power of waves and
tides on the sea-coast. But the rate of waste is very unequal, since the level
and gently sloping lands, where they are protected by a continuous covering of
vegetation, escape nearly all wear and tear, so that they may remain for ages in
a stationary condition, while the removal of matter is constantly widening and
deepening the intervening ravines and valleys.
The materials, both fine and coarse, carried down annually by rivers from the
higher regions to the lower, and deposited in successive strata in the basins of
seas and lakes, must be of enormous volume. We are always liable to underrate
their magnitude, because the accumulation of strata is going on out of sight.
There are, however, causes at work which, in the course of centuries, tend to
render visible these modern formations, whether of marine or lacustrine origin.
For a large portion of the earth's crust is always undergoing a change of level,
some areas rising and others sinking at the rate of a few inches, or a few feet,
perhaps sometimes yards, in a century; so that spaces which were once subaqueous
are gradually converted into land, and others which were high and dry become
submerged. In consequence of such movements we find in certain regions, as in
Cashmere, for example, where the mountains are often shaken by earthquakes,
deposits which were formed in lakes in the historical period, but through which
rivers have now cut deep and wide channels. In lacustrine strata thus
intersected, works of art and fresh-water shells are seen. In other districts on
the borders of the sea, usually at very moderate elevations above its level,
raised beaches occur, or marine littoral deposits, such as those in which, on
the borders of the Bay of Baiae, near Naples, the well-known temple of Serapis
was imbedded. In that case the date of the monument buried in the marine strata
is ascertainable, but in many other instances the exact age of the remains of
human workmanship is uncertain, as in the estuary of the Clyde at Glasgow, where
many canoes have been exhumed, with other works of art, all assignable to some
part of the Recent Period.
DANISH PEAT AND SHELL-MOUNDS OR KITCHEN-MIDDENS.
Sometimes we obtain evidence, without the aid of a change of level, of events
which took place in pre-historic times. The combined labours, for example, of
the antiquary, zoologist, and botanist have brought to light many monuments of
the early inhabitants buried in peat-mosses in Denmark. Their geological age is
determined by the fact that, not only the contemporaneous fresh-water and land
shells, but all the quadrupeds, found in the peat, agree specifically with those
now inhabiting the same districts, or which are known to have been indigenous in
Denmark within the memory of man. In the lower beds of peat (a deposit varying
from 20 to 30 feet in thickness), weapons of stone accompany trunks of the
Scotch fir, Pinus sylvestris. This peat may be referred to that part of the
stone period for which Sir John Lubbock proposed the name of "Neolithic" in
contradistinction to a still older era, termed by him "Paleolithic," and which
will be described in the sequel. (Sir John Lubbock Pre-historic Times page 3
1865.) In the higher portions of the same Danish bogs, bronze implements are
associated with trunks and acorns of the common oak. It appears that the pine
has never been a native of Denmark in historical times, and it seems to have
given place to the oak about the time when articles and instruments of bronze
superseded those of stone. It also appears that, at a still later period, the
oak itself became scarce, and was nearly supplanted by the beech, a tree which
now flourishes luxuriantly in Denmark. Again, at the still later epoch when the
beech-tree abounded, tools of iron were introduced, and were gradually
substituted for those of bronze.
On the coasts of the Danish islands in the Baltic, certain mounds, called in
those countries "Kjokken-modding," or "kitchen-middens," occur, consisting
chiefly of the castaway shells of the oyster, cockle, periwinkle, and other
eatable kinds of molluscs. The mounds are from three to ten feet high, and from
100 to 1000 feet in their longest diameter. They greatly resemble heaps of
shells formed by the Red Indians of North America along the eastern shores of
the United States. In the old refuse-heaps, recently studied by the Danish
antiquaries and naturalists with great skill and diligence, no implements of
metal have ever been detected. All the knives, hatchets, and other tools, are of
stone, horn, bone, or wood. With them are often intermixed fragments of rude
pottery, charcoal and cinders, and the bones of quadrupeds on which the rude
people fed. These bones belong to wild species still living in Europe, though
some of them, like the beaver, have long been extirpated in Denmark. The only
animal which they seem to have domesticated was the dog.
As there is an entire absence of metallic tools, these refuse-heaps are referred
to the Neolithic division of the age of stone, which immediately preceded in
Denmark the age of bronze. It appears that a race more advanced in civilisation,
armed with weapons of that mixed metal, invaded Scandinavia, and ousted the
LACUSTRINE HABITATIONS OF SWITZERLAND.
In Switzerland a different class of monuments, illustrating the successive ages
of stone, bronze, and iron, has been of late years investigated with great
success, and especially since 1854, in which year Dr. F. Keller explored near
the shore at Meilen, in the bottom of the lake of Zurich, the ruins of an old
village, originally built on numerous wooden piles, driven, at some unknown
period, into the muddy bed of the lake. Since then a great many other
localities, more than a hundred and fifty in all, have been detected of similar
pile-dwellings, situated near the borders of the Swiss lakes, at points where
the depth of water does not exceed 15 feet. (Bulletin de la Societie Vaudoise
des Sciences Nat. tome 6 Lausanne 1860; and Antiquity of Man by the author
chapter 2.) The superficial mud in such cases is filled with various articles,
many hundreds of them being often dredged up from a very limited area. Thousands
of piles, decayed at their upper extremities, are often met with still firmly
fixed in the mud.
As the ages of stone, bronze, and iron merely indicate successive stages of
civilisation, they may all have coexisted at once in different parts of the
globe, and even in contiguous regions, among nations having little intercourse
with each other. To make out, therefore, a distinct chronological series of
monuments is only possible when our observations are confined to a limited
district, such as Switzerland.
The relative antiquity of the pile-dwellings, which belong respectively to the
ages of stone and bronze, is clearly illustrated by the associations of the
tools with certain groups of animal remains. Where the tools are of stone, the
castaway bones which served for the food of the ancient people are those of
deer, the wild boar, and wild ox, which abounded when society was in the hunter
state. But the bones of the later or bronze epoch were chiefly those of the
domestic ox, goat, and pig, indicating progress in civilisation. Some villages
of the stone age are of later date than others, and exhibit signs of an improved
state of the arts. Among their relics are discovered carbonised grains of wheat
and barley, and pieces of bread, proving that the cultivation of cereals had
begun. In the same settlements, also, cloth, made of woven flax and straw, has
The pottery of the bronze age in Switzerland is of a finer texture, and more
elegant in form, than that of the age of stone. At Nidau, on the lake of Bienne,
articles of iron have also been discovered, so that this settlement was
evidently not abandoned till that metal had come into use.
At La Thene, in the northern angle of the lake of Neufchatel, a great many
articles of iron have been obtained, which in form and ornamentation are
entirely different both from those of the bronze period and from those used by
the Romans. Gaulish and Celtic coins have also been found there by MM. Schwab
and Desor. They agree in character with remains, including many iron swords,
which have been found at Tiefenau, near Berne, in ground supposed to have been a
battle-field; and their date appears to have been anterior to the great Roman
invasion of Northern Europe, though perhaps not long before that event. (Sir J.
Lubbock's Lecture, Royal Institution February 27, 1863.) Coins, which sometimes
occur in deposits of the age of iron, have never yet been found in formations of
the ages of bronze or stone.
The period of bronze must have been one of foreign commerce, as tin, which
enters into this metallic mixture in the proportion of about ten per cent to the
copper, was obtained by the ancients chiefly from Cornwall. (Diodorus 5, 21, 22
and Sir H. James Note on Block of Tin dredged up in Falmouth Harbour. Royal
Institution of Cornwall 1863.) Very few human bones of the bronze period have
been met with in the Danish peat, or in the Swiss lake-dwellings, and this
scarcity is generally attributed by archaeologists to the custom of burning the
dead, which prevailed in the age of bronze.
From the foregoing observations we may infer that the ages of iron and bronze in
Northern and Central Europe were preceded by a stone age, the Neolithic,
referable to that division of the post-tertiary epoch which I have called
Recent, when the mammalia as well as the other organic remains accompanying the
stone implements were of living species. But memorials have of late been brought
to light of a still older age of stone, for which, as above stated, the name
Paleolithic has been proposed, when man was contemporary in Europe with the
elephant and rhinoceros, and various other animals, of which many of the most
conspicuous have long since died out.
REINDEER PERIOD IN SOUTH OF FRANCE.
In the larger number of the caves of Europe, as for example in those of England,
Belgium, Germany, and many parts of France, the animal remains agree
specifically with the fauna of this oldest division of the age of stone, or that
to which belongs the drift of Amiens and Abbeville presently to be mentioned,
containing flint implements of a very antique type. But there are some caves in
the departments of Dordogne, Aude, and other parts of the south of France, which
are believed by M. Lartet to be of intermediate date between the Paleolithic and
Neolithic periods. To this intermediate era M. Lartet gave, in 1863, the name of
the "reindeer period," because vast quantities of the bones and horns of that
deer have been met with in the French caverns. In some cases separate plates of
molars of the mammoth, and several teeth of the great Irish deer, Cervus
megaceros, and of the cave-lion, Felis spelaea, have been found mixed up with
cut and carved bones of reindeer. On one of these sculptured bones in the cave
of Perigord, a rude representation of the mammoth, with its long curved tusks
and covering of wool, occurs, which is regarded by M. Lartet as placing beyond
all doubt the fact that the early inhabitants of these caves must have seen this
species of elephant still living in France. The presence of the marmot, as well
as the reindeer and some other northern animals, in these caverns seems to imply
a colder climate than that of the Swiss lake-dwellings, in which no remains of
reindeer have as yet been discovered. The absence of this last in the old
lacustrine habitations of Switzerland is the more significant, because in a cave
in the neighbourhood of the lake of Geneva, namely, that of Mont Saleve, bones
of the reindeer occur with flint implements similar to those of the caverns of
Dordogne and Perigord.
The state of the arts, as exemplified by the instruments found in these caverns
of the reindeer period, is somewhat more advanced than that which characterises
the tools of the Amiens drift, but is nevertheless more rude than that of the
Swiss lake-dwellings. No metallic articles occur, and the stone hatchets are not
ground after the fashion of celts; the needles of bone are shaped in a
workmanlike style, having their eyes drilled with consummate skill.
The formations above alluded to, which are as yet but imperfectly known, may be
classed as belonging to the close of the Paleolithic era, of the monuments of
which I am now about to treat.
ALLUVIAL DEPOSITS OF THE PALEOLITHIC AGE.
(FIGURE 87. Recent and Post-pliocene alluvial deposits.
1. Peat of the recent period.
2. Gravel of modern river.
2'. Loam of brick-earth (loess) of same age as 2, formed by inundations of the
3. Lower-level valley-gravel with extinct mammalia (Post-pliocene).
3'. Loam of same age.
4. Higher-level valley-gravel (Post-pliocene).
4'. Loam of same age.
5. Upland gravel of various kinds and periods, consisting in some places of
unstratified boulder clay or glacial drift.
6. Older rocks.)
The alluvial and marine deposits of the Paleolithic age, the earliest to which
any vestiges of man have yet been traced back, belong to a time when the
physical geography of Europe differed in a marked degree from that now
prevailing. In the Neolithic period, the valleys and rivers coincided almost
entirely with those by which the present drainage of the land is effected, and
the peat-mosses were the same as those now growing. The situation of the shell-
mounds and lake-dwellings above alluded to is such as to imply that the
topography of the districts where they are observed has not subsequently
undergone any material alteration. Whereas we no sooner examine the Post-
pliocene formations, in which the remains of so many extinct mammalia are found,
than we at once perceive a more decided discrepancy between the former and
present outline of the surface. Since those deposits originated, changes of
considerable magnitude have been effected in the depth and width of many
valleys, as also in the direction of the superficial and subterranean drainage,
and, as is manifest near the sea-coast, in the relative position of land and
water. In Figure 87 an ideal section is given, illustrating the different
position which the Recent and Post-pliocene alluvial deposits occupy in many
The peat, No. 1, has been formed in a low part of the modern alluvial plain, in
parts of which gravel No. 2 of the recent period is seen. Over this gravel the
loam or fine sediment 2' has in many places been deposited by the river during
floods which covered nearly the whole alluvial plain.
No. 3 represents an older alluvium, composed of sand and gravel, formed before
the valley had been excavated to its present depth. It contains the remains of
fluviatile shells of living species associated with the bones of mammalia, in
part of recent, and in part of extinct species. Among the latter, the mammoth
(E. primigenius) and the Siberian rhinoceros (R. tichorhinus) are the most
common in Europe. No. 3' is a remnant of the loam or brick-earth by which No. 3
was overspread. No. 4 is a still older and more elevated terrace, similar in its
composition and organic remains to No. 3, and covered in like manner with its
inundation-mud, 4'. Sometimes the valley-gravels of older date are entirely
missing, or there is only one, and occasionally there are more than two, marking
as many successive stages in the excavation of the valley. They usually occur at
heights varying from 10 to 100 feet, sometimes on the right and sometimes on the
left side of the existing river-plain, but rarely in great strength on exactly
opposite sides of the valley.
Among the genera of extinct quadrupeds most frequently met with in England,
France, Germany, and other parts of Europe, are the elephant, rhinoceros,
hippopotamus, horse, great Irish deer, bear, tiger, and hyaena. In the peat, No.
1 (Figure 87), and in the more modern gravel and silt (No. 2), works of art of
the ages of iron and bronze, and of the later or Neolithic stone period, already
described, are met with. In the more ancient or Paleolithic gravels, 3 and 4,
there have been found of late years in several valleys in France and England--
as, for example, in those of the Seine and Somme, and of the Thames and Ouse,
near Bedford-- stone implements of a rude type, showing that man coexisted in
those districts with the mammoth and other extinct quadrupeds of the genera
above enumerated. In 1847, M. Boucher de Perthes observed in an ancient alluvium
at Abbeville, in Picardy, the bones of extinct mammalia associated in such a
manner with flint implements of a rude type as to lead him to infer that both
the organic remains and the works of art were referable to one and the same
period. This inference was soon after confirmed by Mr. Prestwich, who found in
1859 a flint tool in situ in the same stratum at Amiens that contained the
remains of extinct mammalia.
The flint implements found at Abbeville and Amiens are most of them considered
to be hatchets and spear-heads, and are different from those commonly called
"celts." These celts, so often found in the recent formations, have a more
regular oblong shape, the result of grinding, by which also a sharp edge has
been given to them. The Abbeville tools found in gravel at different levels, as
in Nos. 3 and 4, Figure 87, in which bones of the elephant, rhinoceros, and
other extinct mammalia occur, are always unground, having evidently been brought
into their present form simply by the chipping off of fragments of flint by
repeated blows, such as could be given by a stone hammer.
Some of them are oval, others of a spear-headed form, no two exactly alike, and
yet the greater number of each kind are obviously fashioned after the same
general pattern. Their outer surface is often white, the original black flint
having been discoloured and bleached by exposure to the air, or by the action of
acids, as they lay in the gravel. They are most commonly stained of the same
ochreous colour as the flints of the gravel in which they are imbedded.
Occasionally their antiquity is indicated not only by their colour but by
superficial incrustations of carbonate of lime, or by dendrites formed of oxide
of iron and manganese. The edges also of most of them are worn, sometimes by
having been used as tools, or sometimes by having been rolled in the old river's
bed. They are met with not only in the lower-level gravels, as in No. 3, Figure
87, but also in No. 4, or the higher gravels, as at St. Acheul, in the suburbs
of Amiens, where the old alluvium lies at an elevation of about 100 feet above
the level of the river Somme. At both levels fluviatile and land-shells are met
with in the loam as well as in the gravel, but there are no marine shells
associated, except at Abbeville, in the lowest part of the gravel, near the sea,
and a few feet only above the present high-water mark. Here with fossil shells
of living species are mingled the bones of Elephas primigenius and E. antiquus,
Rhinoceros tichorhinus, Hippopotamus, Felis spelaea, Hyaena spelaea, reindeer,
and many others, the bones accompanying the flint implements in such a manner as
to show that both were buried in the old alluvium at the same period.
Nearly the entire skeleton of a rhinoceros was found at one point, namely, in
the Menchecourt drift at Abbeville, the bones being in such juxtaposition as to
show that the cartilage must have held them together at the time of their
The general absence here and elsewhere of human bones from gravel and sand in
which flint tools are discovered, may in some degree be due to the present
limited extent of our researches. But it may also be presumed that when a hunter
population, always scanty in numbers, ranged over this region, they were too
wary to allow themselves to be overtaken by the floods which swept away many
herbivorous animals from the low river-plains where they may have been pasturing
or sleeping. Beasts of prey prowling about the same alluvial flats in search of
food may also have been surprised more readily than the human tenant of the same
region, to whom the signs of a coming tempest were better known.
INUNDATION-MUD OF RIVERS.-- BRICK-EARTH.-- FLUVIATILE LOAM, OR LOESS.
As a general rule, the fluviatile alluvia of different ages (Nos. 2, 3, 4,
Figure 87) are severally made up of coarse materials in their lower portions,
and of fine silt or loam in their upper parts. For rivers are constantly
shifting their position in the valley-plain, encroaching gradually on one bank,
near which there is deep water, and deserting the other or opposite side, where
the channel is growing shallower, being destined eventually to be converted into
land. Where the current runs strongest, coarse gravel is swept along, and where
its velocity is slackened, first sand, and then only the finest mud, is thrown
down. A thin film of this fine sediment is spread, during floods, over a wide
area, on one, or sometimes on both sides, of the main stream, often reaching as
far as the base of the bluffs or higher grounds which bound the valley. Of such
a description are the well-known annual deposits of the Nile, to which Egypt
owes its fertility. So thin are they, that the aggregate amount accumulated in a
century is said rarely to exceed five inches, although in the course of
thousands of years it has attained a vast thickness, the bottom not having been
reached by borings extending to a depth of 60 feet towards the central parts of
the valley. Everywhere it consists of the same homogeneous mud, destitute of
stratification-- the only signs of successive accumulation being where the Nile
has silted up its channel, or where the blown sands of the Libyan desert have
invaded the plain, and given rise to alternate layers of sand and mud.
In European river-loams we occasionally observe isolated pebbles and angular
pieces of stone which have been floated by ice to the places where they now
occur; but no such coarse materials are met with in the plains of Egypt.
In some parts of the valley of the Rhine the accumulation of similar loam,
called in Germany "loess," has taken place on an enormous scale. Its colour is
yellowish-grey, and very homogeneous; and Professor Bischoff has ascertained, by
analysis, that it agrees in composition with the mud of the Nile. Although for
the most part unstratified, it betrays in some places marks of stratification,
especially where it contains calcareous concretions, or in its lower part where
it rests on subjacent gravel and sand which alternate with each other near the
junction. About a sixth part of the whole mass is composed of carbonate of lime,
and there is usually an intermixture of fine quartzose and micaceous sand.
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