REMARKS ON VARIOUS QUESTIONS.
There are many problems connected with geology which can only be
solved by detailed study of the stratified rocks, and when solved the
principles of the science will be more fully elucidated. In the
present state of our knowledge some of these problems are ripe for
discussion, others can merely be indicated, while others again have
probably remained hidden, though it will be the task of the geologist
of the future to clear them up. Among the many questions which demand
knowledge of stratigraphical geology for their right understanding are
the following, which will be briefly considered in this chapter:--the
changes in the position of land and sea in past times, and the growth
of continents; the replacement of a school of uniformitarianism by one
of evolutionism; and the duration of geological time.
_Changes in the position of land and sea._ Certain physicists have
arrived at the conclusion that the general position of our oceans and
continents was determined at a very early period in the earth's
history, and that the changes which have occurred in their position
since then have been comparatively insignificant. The wide extent of
land over which stratified rocks are distributed at once indicates
that from the point of view of the geologist the changes have been
very important, and it is worth inquiring whether they are not
sufficiently important to prove that the primitive oceans and
continents have undergone so much alteration as to be unrecognisable.
Some authorities, while recognising the great changes which have
occurred in the relative position of land and sea during those periods
of which geologists have direct information, suppose that the changes
took place to a large degree in certain 'critical areas' bordering the
more stable areas of permanent ocean on the one side and permanent
land on the other.
In discussing the question of general permanence of land and ocean
regions it will be convenient to commence with a study of the present
land areas, and at the outset we may take into consideration the
present distribution of marine sediment over different parts of the
land, using the last edition of M. Jules Marcou's geological map of
the world for the purpose[119]. A glimpse at this map indicates that
more than half of the land areas are occupied by rocks which are as
yet unknown (many of which _may_ be marine sediments), or by
crystalline schists of which the mode of origin has not yet been fully
explained, so that a large part of Central Asia, the interior of
Africa, and of South America may have existed as land from very early
times, and the same may be said of smaller portions of Europe and
North America. Actual observation of a geological map therefore
indicates the possibility that about half of the land surfaces may
have existed as such through very long periods, but though there is a
possibility of this, the probability is not very great. The unknown
regions, as remarked above, may consist to a considerable extent of
marine sediments, and the existence of isolated patches of late
Palæozoic and of Mesozoic strata in the heart of Central Asia, points
to the submergence of much wider regions than those in which these
isolated patches have been found. Again, the character of the
sediments when they abut against the crystalline schists frequently
proves that these sediments once extended further over the crystalline
schists, and have since been removed by denudation, so that even if we
assume that the crystalline schists are all of very early date, and
not necessarily formed in any case from marine sediments, we cannot
suppose that all the area occupied by them has existed as land for
long periods of time. On the other hand, the major part of Europe and
North Africa, extensive tracts in Asia, the greater part of Australia,
a very large part of North America and considerable tracts of South
America give proofs of having been occupied by the oceans in Palæozoic
and later times.
[Footnote 119: A reduced copy of this map will be found opposite the
title-page of the first volume of Prof. Prestwich's _Geology_.]
It may be answered that most of these regions containing marine
sediments occur in critical areas, which have undergone a certain
amount of oscillation owing to earth-movements, and that the interior
parts of the great continental masses have been practically
stationary. But if these lands had been land-areas through geological
ages they must have been acted upon by the agents of subaerial
denudation, throughout these ages, and long ago reduced to
peneplains[120] unless the action of these subaerial agents was
counteracted by that of elevating forces, but if these forces were
sufficient to counteract the action of subaerial denudation through
countless ages, they were also sufficient to raise extensive tracts
of land above sea-level, and materially to alter the distribution of
land and sea, and if elevation could go on to this extent, why not
also depression?
[Footnote 120: A term proposed by Prof. W. M. Davis for a nearly level
surface of subaerial denudation, as opposed to a plain of marine
denudation.]
Proceeding a step further, and examining the character of the
sediments as well as their geographical distribution, we find
further evidence of great crust-movements. It has been urged that
deep-water sediments do not occur amongst the strata found on the
continents,--that there are no representatives of the abysmal deposits
of recent ocean floors amongst the strata of the geological
column[121], but the researches of the last two decades have brought
to light foraminiferal and radiolarian deposits, pteropodal deposits,
and possibly deep-sea clays, which are comparable with those in
process of formation at great depths in existing oceans, and though
the proofs of their deep-sea origin are not always as full as might be
desired in the case of the older rocks[122], we can speak with greater
certainty when we examine those of Tertiary age, and if the deep-sea
accumulations of this late date can be uplifted above sea-level, this
is much more likely to have occurred with those of past times. When a
deposit like the radiolarian rock of Barbadoes, the deep-water
character of which has been conclusively proved, can be elevated into
land since Miocene or possibly Pliocene times, it is evident that the
crust-movements have been sufficient to produce the most profound
changes in the distribution of land and sea during the long ages which
are known to us. Another argument against the occurrence of extensive
changes has been derived from an examination of those islands which
are spoken of as oceanic islands. Strictly speaking an oceanic island
is one in which the present fauna and flora give indications of their
introduction by transport across intervening sea, and no indications
of the existence of forms of life which inhabited it when it was once
united to a continent; it may be inferred with a considerable degree
of certainty that these islands have been isolated for long periods of
time. It has been stated that these oceanic islands never contain
marine sediments of any considerable degree of antiquity, and that
there are therefore no traces of former continents over those wide
tracts of ocean which are occupied by oceanic islands. The evidence is
of a negative character. The islands would be less likely to exhibit
ancient sediments than continents, for being near the ocean, they
would be readily submerged, and the older deposits masked by newer
ones, though this need not necessarily account for the entire absence
of ancient rocks amongst them. The danger of the argument lies in the
fact that we do not yet know how far these old rocks really are
absent, as the geology of the oceanic isles has not been fully
explored from this point of view, and already several cases of the
asserted presence of ancient rocks on these islands have been
recorded.
[Footnote 121: See Mr A. R. Wallace's _Island Life_.]
[Footnote 122: See chapter IX.]
The argument derived from the present distribution of organisms is far
too complex to be discussed here, and the student is recommended to
read a masterly review of the evidence in Dr W. T. Blanford's
Presidential Address to the Geological Society in 1890, on the
question of the Permanence of Ocean Basins[123]. After reviewing the
evidence furnished by a study of modern distribution he concludes that
it "is far too contradictory to be received as proof of the permanence
of oceans and continents."
[Footnote 123: _Quart. Journ. Geol. Soc._, vol. XLVI., _Proc._, p.
59.]
The existence of former extensive land tracts over regions now
occupied by sea is naturally more difficult to prove than that of sea
over land, as we depend upon inference rather than actual observation
to a much greater degree than when considering the permanence of
continents, nevertheless a considerable amount of indirect evidence in
favour of the existence of widespread land tracts over our present
ocean regions has been accumulated and will be briefly noticed. We may
take first the evidence derived from the nature of sediments, and
afterwards that which has been acquired by studying distribution of
organisms in past times.
The indications of existence of an extensive tract of continent over
the North Atlantic Ocean, during Palæozoic times have already been
considered, and it was seen that the thinning out of the Palæozoic
sediments when traced away from the present Atlantic borders in an
easterly direction over Europe and in a westerly one over North
America pointed to the existence of this Palæozoic 'Atlantis,' as
maintained by Prof. Hull in his work, "Contributions to the Physical
History of the British Isles." This writer gives some reasons for
supposing that the continental mass began to break up towards the end
of Palæozoic times, though it is not clear that complete replacement
of land by sea occurred, and the nature of the Wealden deposits has
been pointed to as evidence of the existence of an extensive tract of
land to the west of Britain during the Cretaceous period.
The Palæontological evidence in favour of destruction of ancient
continental areas and their replacement by the sea is more
satisfactory than that which is based on physical grounds. The
distribution of the Glossopteris flora of the Permo-Carboniferous
period points to the former existence of a great southern continent,
including the sites of Australia, India, South Africa and South
America,--the Gondwanaland of Prof. E. Suess[124].
[Footnote 124: On this question and that of the other destroyed
continental areas noted here, see W. T. Blanford's _Presidential
Address_, _loc. cit._]
Again, a study of Jurassic and Cretaceous faunas has led
palæontologists to conclude that there was a connexion betwixt S.
Africa and India in Mesozoic times across a portion of the area now
occupied by the Indian Ocean, and also between S. Africa and S.
America, and these inferences are supported by study of the
distribution of existing forms.
The sudden appearance of the Dicotyledonous Angiosperms in Upper
Cretaceous rocks has also been used as evidence of destruction of
considerable tracts of land subsequently to Upper Cretaceous times,
and there is a certain amount of evidence in favour of the existence
of this land in the north polar region, in an area now largely
occupied by water, though relics of it are left, as the Faroe Isles,
Spitsbergen, Novaya Zembla and Franz Josef Land.
I cannot conclude the consideration of the question of permanence of
oceans and continents more fitly than by quoting from Dr Blanford's
address. He says, "There is no evidence whatever in favour of the
extreme view accepted by some physicists and geologists that every
ocean-bed now more than 1000 fathoms deep has always been ocean, and
that no part of the continental area has ever been beneath the deep
sea. Not only is there clear proof that some land-areas lying within
continental limits have at a comparatively recent date been submerged
over 1000 fathoms, whilst sea-bottoms now over 1000 fathoms deep must
have been land in part of the Tertiary era, but there are a mass of
facts both geological and biological in favour of land-connexion
having formerly existed in certain cases across what are now broad and
deep ocean[125]."
[Footnote 125: _Loc. cit._, _Proc._ p. 107.]
_Growth of continents._ Whatever view as to the general permanence of
continents and oceans be ultimately established, the occurrence of
widespread changes in the position of land and sea is indisputable,
and it is of interest for us to consider the nature of these changes
in the formation of continents. Prof. J. D. Dana has put forward a
hypothesis of growth of continents by a process of accretion, causing
diminution in the oceanic areas, which at the same time became deeper:
such growth need not always take place in exactly the same way, and
study of the distribution of the strata of the North American
continent suggests that the growth there was endogenous, the older
rocks lying to the west and north forming a horseshoe shaped continent
enclosing a gulf-like prolongation of the Atlantic, which became
contracted by deposition and uplift in successive geological periods,
though it is still partly existent as the Gulf of Mexico. The Eurasian
continent, especially its western portion, suggests more irregular
growth around scattered nuclei of older rocks, though the process is
not completed, and many gulf-like prolongations, as the Baltic and the
Mediterranean, still remain as water-tracts, which have not yet been
added to the continents.
Although extensive additions to continents may be and no doubt are
often largely due to epeirogenic movements, the influence of orogenic
movements on continent-formation is very pronounced. As the result of
orogenic movements, the rocks of portions of the earth's crust become
greatly compressed, and give rise to masses which readily resist
denudation; moreover, these comparatively rigid masses, as shown by M.
Bertrand, tend to undergo elevation along the same lines as those
which formed the axes of previous elevations, and accordingly after a
continental area has undergone denudation for a considerable period,
the uplands consist of rocks which have undergone orogenic
disturbance, while the tracts of ground which are occupied by rocks
which have not suffered disturbances of this character, even if
originally uplifted far above sea-level, tend to be destroyed, and
ultimately occupied by tracts of ocean. Stumps of former mountain
chains may be again and again established as nuclei of continents and
as every period of orogenic movement will add to the number of these
nuclei, the continental areas must in course of time become more
complex in structure. Moreover, as some areas are affected by orogenic
movements to a greater extent than others, the complexity of different
continental masses will vary. Thus, western Europe has been affected
by orogenic movements during many periods since the commencement of
Cambrian times and its structure is extremely complex, while the
central and western parts of Russia have not been subjected to violent
orogenic disturbances since Cambrian times, and accordingly we find
the structure of that area comparatively simple; the greater part of
Africa seems to have escaped these movements since remote times, and
the structure of that continent is extremely simple when compared with
the Eurasian continental tract. It need hardly be stated that the
formation of extensive chains composed of volcanic material, by
accumulation of lavas and ashes on the earth's surface, may give and
often has given rise to more rigid tracts, which will bring about the
same effects as those produced by orogenic disturbance as illustrated
on a small scale by the Lower Palæozoic volcanic rocks of Cambria and
Cumbria.
_Uniformitarianism and Evolution._ According to the extreme
uniformitarian views held by some geologists, the agents which are in
operation at the present day are similar in kind and in intensity to
those which were at work in past times, though no geologist will be
found who is sufficiently bold to assert that this holds true for all
periods of the earth's history, but only for those of which the
geologist has direct information derived from a study of the rocks,
and he is content to follow his master Hutton in ignoring periods of
which he cannot find records amongst the rocks. The modern geologist,
however, while rightly regarding the rocks as his principal source of
information finds that he cannot afford to ignore the evidence
furnished by the physicist, chemist, astronomer and biologist, which
throws light upon the history of periods far earlier than those of
which he has any records preserved amongst the outer portions of the
earth itself, just as the modern historian is not content with written
records, but must turn to the 'prehistoric' archæologist and geologist
for information concerning the history of early man upon the earth.
Interpreting the scope of geology in this general way, rigid
uniformitarianism must be abandoned. Assuming that the tenets of the
evolutionist school are generally true, the question is, how far does
this affect the geologist in his study of those periods of which we
have definite records amongst the rocks? This is a question which
cannot readily be answered at the present day, for our study of the
rocks is not sufficiently far advanced to enable us to point out
effects amongst the older rocks which were clearly caused by agents
working with greater intensity than they do at present, but as, on
the other hand, we cannot prove that these effects are due to agents
working with no greater intensity than that which now marks these
operations, it is unphilosophical to assume the latter. No student of
science at the present day would state that because there has been no
observed case of incoming of fresh species within the time that man
has actually observed the present faunas and floras, the hypothesis of
evolution of organisms is disproved, for the time of observation has
been too short, and similarly the time which has elapsed since the
formation of, say, the Cambrian rocks may have been too short, as
compared with the time which has elapsed since the formation of the
earth, to allow of any important change in the operation of the
geological agents.
Leaving out of account, for the moment, the actual evidence which has
been derived from a study of the rocks, we may briefly consider the
theoretical grounds upon which the substitution of an evolutionist
school of geology for one of uniformity has been suggested[126]. The
principal sources of energy which have exerted an influence upon
geological changes are the heat received from the sun and that given
off from the earth itself, both of which must have diminished in
quantity throughout geological ages. To the former source we largely
owe climatic changes and the operations of denudation, and accordingly
of deposition; to the latter, those of earth-movement and vulcanicity.
It by no means follows that because the agents were once potentially
more powerful than now, they would necessarily produce greater
effects, for that depends to some extent upon the various conditions
which prevailed at different times. To give an example:--if there had
at any time been a universal ocean of considerable depth, however
active the agents of denudation were then, they could produce no
effect whatever, having nothing to work upon; to take a less extreme
case, if our continents at any past time were smaller and less
elevated than at present, agents of denudation working with greater
intensity than that of the present agents need not necessarily have
produced a greater amount of denudation than that which is going on at
the present day. Again, let us consider vulcanicity: "It is as
certain," says Lord Kelvin, "that there is less volcanic energy in the
whole earth than there was a thousand years ago, as it is that there
is less gunpowder in a 'Monitor' after she has been seen to discharge
shot and shell, whether at a nearly equable rate or not, for five
hours without receiving fresh supplies than there was at the beginning
of the action." But it does not follow that the manifestations of
volcanic activity were necessarily more violent in early geological
times than now, for the degree of violence would be affected by other
things than the volcanic energy, such as the thickness of the earth's
crust.
[Footnote 126: The student may consult an interesting article by Prof.
Sollas bearing on this subject. See _Geol. Mag._ Dec. 2, vol. IV. p.
1.]
And now, let us consider briefly the characters of the rocks of the
crust, to see if they throw any light upon this question. The earliest
sediments of which we have any certain knowledge resemble in a
striking manner those formed at the present day, and they seem to have
been formed under very much the same conditions, though further work
may show that there were somewhat different conditions which did
produce definite differences in the characters of the earlier
strata[127]. Our knowledge of earth-movement and vulcanicity which
took place in past times is still too small to enable us to draw any
certain conclusions connected with the subject under discussion from
it. Perhaps the most suggestive indication of one set of conditions
having been generally similar in those early periods of which we have
definite records amongst the rocks is furnished by study of past
climate. If we accept the nebular hypothesis as a starting point, we
must admit that in the early stages of the earth's history the
temperature of the surface, which would then be largely dependent upon
the amount of heat given out from the earth itself as well as upon
that received from the sun, must have been much higher than it is at
the present day, and indeed the mere diminution of the amount of heat
received from the sun would probably be sufficient to account for a
very marked lowering of the temperature. Besides this change of
temperature, resulting in gradual lowering of temperature over the
whole earth's surface, we have other changes dependent upon different
conditions, as proved by the fact, that there have been alternations
of glacial and genial periods. If the general temperature had been
very high in the early periods of which we have actual records, the
oscillations would not be sufficient to produce a lowering of
temperature sufficient to cause glacial periods, whereas if it had not
been appreciably higher than now, glacial periods might be produced.
This may be represented diagrammatically.
[Footnote 127: On this matter see Teall, J. J. H., 'Presidential
Address to Section C,' _Report of the British Association_, 1893.]
Let _a_ represent the temperature at the commencement of earth-history
and _b_ that necessary for glaciation, and _bc_ the lapse of time
between then and now. The curved line indicates the gradual fall in
temperature due to diminution of the amount of heat, while the zigzag
line represents the oscillations due to secular climatic changes. If
the Cambrian period x occurred comparatively soon after the
commencement of earth-history as shown in fig. _A_, no glaciation
could be produced, even during periods when secular changes caused
colder conditions than the mean, whereas if the Cambrian period
occurred at a time very remote from the commencement of earth-history
as shown in _B_, glacial conditions could be produced then as now, for
the mean temperature, as shown by the distance of the curve from the
line _bc_, would be practically as it now is. The studies of the last
few decades have brought into prominence the occurrence of glacial
periods in remote times, probably in early Palæozoic times; and as far
as the mean temperature of the earth's surface is concerned, it would
appear, from the knowledge in our possession, that matters were not
very different in those early times from what they now are.
[Illustration: Fig. 25.]
Some further remarks will be made in subsequent paragraphs concerning
the period of the earth's history at which the geologist is first
furnished with definite records, but in the meantime it may be
observed that the geologist will do well, when working amongst the
strata, to consider that the more active operation of agents, even in
times of which he has definite knowledge, may have produced effects
which he should be prepared to discover, as their discovery would be
of considerable importance, and that he should not be content to infer
that because it has been proved that agents operating with the same
intensity as that which they have at present, _may_ have produced all
the effects which he can actually observe, they therefore necessarily
_did_ produce them.
_Recurrences._ Absolute uniformity of conditions is impossible, even
in a single area. Every change which takes place upon the earth
produces conditions somewhat dissimilar from those which previously
existed, and these will leave their effects upon the physiography of
the area. For this reason, assuming that the conditions have gradually
changed from simpler to more complex, every period of time will have
been marked by conditions which never prevailed before or afterwards,
and these will leave their impress upon the deposits of the period. It
is doubtful for instance, as already remarked, whether the exact
conditions which gave rise to the extensive deposits of vegetable
matter in Carboniferous times which now form coal, ever occurred to a
like extent in previous or subsequent periods, and accordingly, though
we have deposits of coal of other ages, none are so extensive as those
of the Coal Measures. Again, as the strata of one period are largely
composed of denuded particles of pre-existing strata, which were
derived directly or indirectly from igneous rock, the soluble material
existing in the igneous rocks must have been gradually eliminated
unless restored by other processes, and we might expect to find that
early sediments have, on the whole, a larger proportion of soluble
silicates than the later ones.
Besides these changes, there are physical changes which are recurrent,
and cause conditions generally similar to pre-existing ones to occur
in an area after an interval of dissimilar ones. We have seen that
deposits tend to vary according to the distance from the coast,
limestone being succeeded by mud, this by sand and gravel, and after
subsidence the sand and gravel are succeeded by mud, and that by
limestone. These changes will produce some effect upon the organisms,
and the recurrence of organisms is a well-known event, of which cases
have been cited in a former chapter.
Again we find, as already pointed out, recurrence of climatic changes,
with alternation of glacial and warmer periods, and these may have
been very widespread, and would influence the other physical
conditions, as well as the distribution of the organisms. Vulcanicity
may have been more rife at some periods than others, for instance
there seems, in the present imperfect state of our knowledge, evidence
of enfeebled vulcanicity in later Mesozoic times, and of its renewed
activity in Tertiary times. Again, orogenic movements seem to have
occurred more extensively at some times than others, as for instance
in early upper Palæozoic times, at the end of the Palæozoic epoch, and
in early Tertiary times, though this may also be an apparent and not
an actual truth, due to imperfect knowledge. In any case, in limited
areas, there seem to have been alternations of periods of uplift
accompanied by marked orogenic movements, and of widespread
depression, accompanied by sedimentation.
The subject of rhythmic recurrence is worthy of further study. This
recurrence in combination with evolutionary change may account for the
apparent marked difference between Cambrian and Precambrian times, a
difference which strikes some geologists as being too great to be
accounted for as due to our ignorance only.
_Organic evolution._ This subject is too wide for more than passing
notice in a work of this character. The evidence of Palæontology is of
extreme importance to the biologist, and indeed, the way in which
evolution of organisms has occurred can only be actually demonstrated
by reference to Palæontology, and the study of Palæontology has
already given much information concerning the lines on which evolution
has proceeded in different groups of organisms. It must be remembered
that the major divisions of the invertebrata were in existence in very
early times; indeed representatives of most of them are found in the
rocks containing the earliest known fauna, that of the _Olenellus_
beds of Cambrian age. If our present views as to evolution be correct,
there is no doubt that the period which elapsed between the appearance
of life upon the globe and the existence of the _Olenellus_ fauna must
have been very great, possibly, as Huxley suggested, much greater than
that which has elapsed between early Cambrian times and the present
day. If this be so, however probable it is that we shall carry our
knowledge of ancient faunas far back beyond Cambrian times, it is
extremely improbable that we shall ever get traces of the very
earliest faunas which occupied our earth.
_Geological time._ Various attempts have been made to give numerical
estimates of the lapse of time which occurred since the earth was
formed, or since the earliest known rocks were deposited. These
attempts may be classed under two heads, namely, those made by
physicists, mainly on evidence obtained otherwise than by a study of
the rocks, and those made by geologists by calculating the mean rate
of denudation and deposition of the rocks, and estimating the average
thickness of the rocks of the geological column.
The calculations of physicists as to the age of the earth vary:--Lord
Kelvin assigned 20,000,000 years as the minimum and 100,000,000 as the
maximum duration of geological time. Prof. Tait has halved Lord
Kelvin's minimum period, while Prof. G. Darwin admits the possibility
of the lapse of 500,000,000 years.
The estimates made by geologists, which will appeal more directly to
the geological student, also vary considerably, though they bear some
proportion to those which have been put forward by the physicists.
Prof. S. Haughton[128] assigned a period of 200,000,000 years for the
accumulation of the rocks of the geological column; Mr Clifton
Ward[129] one of 62,000,000 years, after studying the rocks of the
English Lake District, and allowing for the gaps in the succession; Mr
A. R. Wallace[130] further lowers the time for the formation of the
column to 28,000,000 years; Sir A. Geikie[131] gives 73,000,000 years
as the minimum and 680,000,000 as the maximum; while Mr J. G.
Goodchild has lately[132] estimated the period at over 700,000,000
years.
[Footnote 128: _Nature_, vol. XVIII. p. 268.]
[Footnote 129: Ward, J. C., 'The Physical History of the English Lake
District,' _Geol. Mag._ Dec 2, vol. VI. p. 110.]
[Footnote 130: Wallace, A. R., _Island Life_, Chap. X.]
[Footnote 131: Geikie, Sir A., 'Presidential Address to the British
Association,' _Report Brit. Assoc._, 1892.]
[Footnote 132: Goodchild, J. G., _Proc. Roy. Soc. Edinburgh_, vol.
XIII. p. 259.]
Interesting as these figures are, they probably convey little to the
ordinary reader, and it is doubtful whether the geologist is really
affected by them to any extent when picturing to himself the vast
duration of geological time. One numerical estimate probably does
impress him, namely that made by Croll as to the date of the Great Ice
Age, for if the Ice Age be so remote as Croll imagined, the
commencement of earth-history must be inconceivably more remote; as
Croll's estimate is not generally accepted, it is doubtful how far
geologists are thus influenced, and probably the fact which does
impress them most, leaving fossils out of account, is the very little
change which has occurred in historic or even in prehistoric times as
compared with the vast changes which are familiar to them after
studying the strata of the geological column.
It is, after all, the succession of varied faunas which really gives
students of the rocks the most convincing proof of the vast periods of
geological time. If anyone doubts this assertion, let him consider
what impression would be made upon him by observing the several
thousand feet of strata of the column if none of them contained any
organisms. Cognisant as he is of the slow rate of change of existing
organisms, the fact that fauna has succeeded fauna in past times
brings home to him in an unmistakeable manner the great antiquity of
the earliest fossiliferous rocks, and as our detailed knowledge of
these faunas increases the impression of great lapse of time is
intensified. And if the earliest fossiliferous rocks be of such vast
antiquity, and, as has been remarked, the period of their formation is
comparatively recent with reference to the actual commencement of
earth-history, the latter must indeed be inconceivably remote, and
numerical estimates can do but little to familiarise us with the
significance of the vast time which has rolled by since the world's
birthday.
INDEX.
Abraum salts, 212
Æolian rocks, 24, 99, 100
Age, definition of, 60
Albian series, 236, 238
Algonkian rocks, 144
Ampthill clay, 232
Angelin, N. P., 161, 162, 165
Aptian series, 236, 237
Aqueous rocks, 24
Archæan rocks, 132
Ardmillan series, 170
Ardwick stage, 192
Arenaceous rocks, 29
Arvonian rocks, 141
Asaphus fauna, 165
Ashgill series, 164, 165, 167-169
Ashprington series, 184
Astian series, 256
Atlantis, 283
Aveline, W. T., 164
Aymestry limestone, 175, 176
Bagshot beds, 244, 246
Bajocian series, 227, 231
Bala limestone, 167
Bala series, 164
Barr series, 170
Barrande, J., 53, 55, 159, 161, 163
Barrois, C., 239
Barrow, G., 138
Barton beds, 244
Bath oolites, 226
Bathonian series, 227, 231
Bed, 27
Bedding plane, 27
Bell, A., 257
Belt, T., 153, 162
Bembridge beds, 251
Bertrand, M., 87, 286
Birkhill shales, 177
Black Jura, 226
Blake, J. F., 138-140
Blanford, W. T., 206, 208, 217, 282, 284
Bonney, T. G., 76, 141, 142
Boulder clay, 262
Bracklesham beds, 244
Bradford clay, 230
Break, palæontological, 61;
physical, 60
Bristow, H., 239
Brockram, 211
Brögger, W. C., 161-163
Brongniart, H., 18
Brongniart, C., 200
Bronze age, 275-277
Brown Jura, 226
Bunter sandstone, 218, 220-222
Bure valley beds, 256
Buttery clay, 276
Caerfai beds, 152, 154, 156
Calcareous rocks, 29
Caldicote series, 139
Callaway, C., 138-140
Callovian series, 227, 232
Cambrian faunas, 158-163
Cambrian system, 152-163
Caradoc series, 165, 168-171
Carbonaceous rocks, 29
Carboniferous fauna and flora, 199-201
Carboniferous limestone, 192, 194, 195
Carboniferous system, 192-201
Carnic beds, 225
Cataclastic rocks, 24
Cave man, 268
Cenomanian series, 236
Ceratopyge fauna, 162
Chalk, 236, 238, 239
Chalk marl, 236
Chemically-formed rocks, 29, 101
Chillesford crag, 256
Chronological terms, 60
Clastic rocks, 24
Climatic conditions, 103, 112, 290, 291
Climatic zones, in Jurassic times, 233;
in Cretaceous times, 241
Clymenian beds, 183
Coal, 196-199
Coal measures, 192;
mode of formation of, 195-199
Coblenzian beds, 184
Collyweston slate, 231
Colonies, theory of, 55
Contemporaneity of strata, 48
Continents, growth of, 285-287
Cope, E., 249
Corallian series, 227, 232
Coralline crag, 256, 257
Cornbrash, 230
Cornstones, 186
Coutchiching series, 144
Crags, 256-259
Cretaceous fauna and flora, 241-243
Cretaceous system, 236-243
Croll, J., 265, 295, 296
Cromer Forest series, 100, 256, 259
Cromer till, 262
Cucullæa beds, 183
Cuvier, Baron G., 18, 20
Dalradian rocks, 137
Dana, J. D., 285
Danian series, 236
Darwin, C., 20, 76
Darwin, G., 295
Daubrée, A., 88
David, T. W. E., 206
Davis, W. M., 258, 280
Dawkins, W. B., 266, 268, 270, 272, 277
Deep-sea deposits, 109
De Hayes, G. P., 19
De la Beche, Sir H., 92
Deposition, order of, 37, 116
Derivative rocks, 23
Devonian flora and fauna, 189-191
Devonian system, 183-191
Dictyograptus fauna, 162
Dimetian rocks, 141
Dogger, 226
Downtonian beds, 175
Dwyka conglomerate, 206
Edwards, F. E., 250
Eifelian beds, 184
Encrinurus fauna, 185
Englacial deposits, 261
Entomis slates, 183
Eocene fauna and flora, 248, 249
Eocene rocks, 244-250
Eozoon canadense, 143
Eparchæan rocks, 132
Epeirogenic movements, 32
Epiclastic rocks, 24;
simulation by cataclastic rocks, 38, 80
Epoch, definition of, 60
Estuarine series, 230
Etheridge, R., 19
Ettingshausen, Baron von, 250
Evans, Sir J., 266, 270, 274, 277
Evolution, 287, 293
Feistmantel, O., 208
Fenland, 276
Fluvio-glacial deposits, 261
Foreland grits, 184
Forest marble, 230
Forest period, 260, 275-277
Fossils, 42;
strata identifiable by, 40;
mode of occurrence of, 44;
relative value of, 47;
remanié, 52;
geographical distribution of, 55;
as indicative of physical conditions, 104
Fossil zone, 67
Foster, C. Le N., 239
Fox, H., 195
Freshwater deposits, 104;
distinction from marine, 105
Fuller's earth, 230
Fusulina beds, 201
Gala beds, 177
Gannister stage, 192
Gardner, J. S., 250
Gault, 236, 238
Geikie, Sir A., 60, 84, 95, 125, 130, 137, 141, 142, 144, 186, 188,
199, 247, 295
Geikie, J., 263
Girvan type, 170
Glacial deposits, permo-carboniferous, 206;
Pleistocene, 260-266
Glacial period, 260-266
Glenkiln shales, 169, 170
Glossopteris flora, 207, 208, 214
Godwin-Austen, R. A. C., 20
Gondwana series, 207
Gondwanaland, 207, 284
Goniatite beds, 183
Goodchild, J. G., 87, 130, 263, 295
Great ice age, 295, 296
Great oolite, 230, 231
Gregory, J. G., 258
Green, A. H., 122, 139, 193
Greensand, Lower, 236;
Upper, 236
Groom, T. T., 178
Gshellian beds, 193, 201
Hampshire basin, 245
Hangman grits, 184
Harker, A., 30, 88
Harkness, R., 161
Harmer, F. W., 258
Harpes fauna, 175
Harrison, W. J., 130
Hartfell shales, 169, 170
Hastings sands, 236, 237
Haughton, S., 295
Headon beds, 251
Heim, A., 32
Hempstead beds, 251
Hercynian systems of folds, 203
Hicks, H., 134, 141, 153, 154, 160, 161, 163, 167, 184, 266
Hickson, S. J., 109
Hill, A., 239
Hill, E., 142
Hilton shales, 210, 211
Hind, W., 196
Hinde, G. J., 169, 195
Hippurite limestone, 241, 242
Hirnant limestone, 167
Homotaxis, 48
Hughes, T. McK., 141, 264, 266
Hull, E., 120, 122, 193, 283
Hume, W. F., 239
Hunt, A. R., 101
Huronian system, 143
Hutton, J., 287
Huxley, T. H., 50, 250
Igneous rocks, 21-23
Ilfracombe beds, 184
Inferior oolite, 230
Inverted strata, 32;
detection of, 32
Iron age, 275, 276
Judd, J. W., 239, 247
Jukes, J. B., 84
Jukes-Browne, A. J., 126, 239, 264
Jurassic beds, 225
Jurassic fauna and flora, 234, 235
Jurassic system, 226-235
Kayser, E., 125, 191
Keewatin series, 144
Kelvin, Lord, 289
Kendall, P., 257
Keuper beds, 218, 221, 222
Kidston, B., 199
Kimmeridge clay, 232
Kimmeridgian series, 226
King, W., 217
Kjerulf, Th., 88
Koninck, L. de, 201
Kupferschiefer, 209
Lake, P., 126, 178
Lamina, 27
Lamplugh, G. W., 80, 119, 264
Lapworth, C., 32, 138, 139, 156, 168-170, 173, 178, 179
Laurentian rocks, 143
Lawson, A. C., 144, 145
Lehmann, J., 77
Lenham beds, 257
Lewis, H. C., 263
Lias, 226, 229
Liassian series, 227, 229
Lincolnshire limestone, 230, 231
Lincombe and Warberry grits, 184
Lindström, G., 114
Lingula flags, 152, 155, 156
Linnarsson, J. G. O., 161
Llandeilo limestone, 167
Llandeilo series, 165, 167
Llandovery series, 174-177
Loess, 267
Logan, Sir W., 20
London Basin, 245
London clay, 113, 244, 246
Longmyndian rocks, 138
Lower London Tertiary beds, 244, 246
Lubbock, Sir J., 270, 277
Ludlow series, 174-176
Lydekker, R., 250
Lyell, Sir C., 6, 12, 19, 106, 129, 224, 263, 270
Lynton slates, 184
McCoy, Sir F., 201
McMahon, C. A., 77
Madsen, H. P., 277
Magnesian Limestone, 209-211
Malm, 226
Maps, geological, 84, 130;
use of, 86, 120, 121
Marcou, J., 130, 279
Marine deposits, 102;
nature of fossils in, 107
Marl slate, 209, 210
Marlstone, 229
Marsh, O. C., 249
Marwood beds, 183
Matthew, G. F., 160-162, 180
Meadfoot sands, 184
Mechanically formed rocks, 29, 102
Mello, J. M., 270
Mendip system of folds, 203
Menevian beds, 152, 154, 156, 161
Metamorphic rocks, 25
Miall, L. C., 122
Michell, J., 10, 11
Millepore oolite, 230, 231
Miller, H., 189
Millet seed sands, 100
Millstone grit, 192
Miocene period, 252-255
Moffat shales, 169, 177
Mojsisovics, E. von, 224, 227
Morgan, C. Ll., 141
Morte slates, 184
Moscovian beds, 193, 301
Mountain limestone, 192
Murchison, Sir R. I., 19, 20, 174, 179
Murray, Sir J., 30
Muschelkalk, 218, 221, 222
Nehring, A., 267, 268
Neobolus fauna, 160
Neocomian series, 236-238
Neolithic age, 275-277
Neumayr, M., 115, 233
Newton, E. T., 45
Nicholson, H. A., 189, 250
Noachian Deluge, 8
Noetling, F., 160
Nordenskjöld, A. E., 113, 114
Noric beds, 225
Northamptonshire sands, 230
Norwich crag, 256, 257
Nummulitic limestone, 248
Old red sandstone, 183, 185, 186, 188, 191
Oldham, R. D., 208
Oldhaven beds, 244, 245
Olenellus fauna, 134, 153, 156-160
Olenus fauna, 152, 161, 162
Oligocene beds, 251, 252
Oligocene fauna and flora, 252
Oolite, 226
Ordovician faunas, 172, 173
Ordovician system, 164-173
Organically formed rocks, 29, 102, 109
Orogenic movements, 32
Osborne beds, 257
Owen, Sir R., 277
Oxford clay, 232
Oxford oolite, 226
Oxfordian series, 227, 232
Palæolithic fauna and flora, 270-274
Palæolithic man, 268, 272-274
Palæolithic period, 267-274
Palæontological break, 61
Palæo-physiography, 120
Paradoxides fauna, 152, 160, 161
Peat deposits, 275, 276
Pebble beds of Bunter, 218
Pebidian rocks, 140
Pengelly, W., 270
Pennant stage, 192
Pennine system of folds, 203
Penrith sandstone, 75, 210, 211
Period, definition of, 60
Permanence of ocean basins, 278-285
Permian fauna and flora, 214-216
Permian system, 209-217
Permo-carboniferous fauna and flora, 207, 208
Permo-carboniferous glacial deposits, 206
Permo-carboniferous period, 205-208
Phillips, J., 10, 11, 201
Physical break, 60
Pickwell Down sandstone, 183
Pilton beds, 183
Plaisancean series, 256
Planes of lamination, 27
Planes of stratification, 27
Pleistocene fauna and flora, 265, 266
Pleistocene period, 260-266
Pliocene fauna and flora, 259
Pliocene period, 256-259
Portland oolites, 226
Portlandian series, 226, 232
Prado, C. de, 161
Precambrian rocks, 132;
mode of formation of, 146
Preller, C. S. du R., 264
Prestwich, Sir J., 19, 130, 279
Productus limestones, 205, 206, 214
Protolenus fauna, 160
Pseudo-stromatism, 76
Purbeckian series, 226, 232
Pyroclastic rocks, 24
Quader sandstone, 240
Ramsay, Sir A. C., 130, 153, 163, 188
Reading beds, 244
Recurrences, 292
Red crag, 256, 257
Reid, C., 45, 257, 264, 268, 271
Renard, A., 30
Reversed fault, 34
Rhætic beds, 218
Rhiwlas limestone, 167
Richthofen, Baron von, 267, 268
Ridley, H. N., 271
River drift man, 268
Rotherham red rock, 202
Rothliegende, 209
Rouelle, 13
St Bees sandstone, 210
St Erth beds, 257
Salopian beds, 175
Salter, J. W., 161, 162, 186
Scarbro' limestone, 230, 231
Schists, crystalline, 76, 77, 133, 147
Scilla, A., 13
Screes, 101
Scrope, G. P., 76
Sections, geological, 84;
use of, 88
Sedimentary rocks, 23
Sedgwick, A., 16, 19, 20, 153, 174
Senonian series, 236
Series, definition of, 60
Seward, A. C., 113, 208
Sigmoidal structure, 33
Siliceous rocks, 29
Silurian faunas, 179, 180
Silurian system, 174-182
Simulation of structures, 72
Sinemurian series, 227, 229
Smith, W., 8, 12-18, 57, 85
Soil, 100
Solenhofen slate, 234
Sollas, W. J., 288
Solva beds, 152, 154, 156, 161
Speckled sandstone, 205, 206
Speeton series, 238
Spencer, H., 50
Spirorbis limestone, 201
Stages, definition of, 60
Steppe period, 260, 267-274
Stonesfield slate, 231
Strachey, J., 10
Strahan, A., 239, 264
Strata, 27;
classification of, 58, 125
Stratification, 26
Stratified rocks, 23;
composition of, 28;
origin of, 29;
classification of, 28, 125;
symbols to represent, 90
Stratigraphical geology, aim of, 1;
W. Smith, founder of, 8, 12-18
Suess, E., 110, 123, 207, 284
Superposition, law of, 31
Surveying, geological, 84
Systems, definition of, 60
Talchir stage, 205, 206
Tarannon shales, 174-177
Teall, J. J. H., 289
Terrestrial rocks, 99
Thanet sands, 244
Thinning out, 28
Thrust plane, 34;
detection of, 35, 82
Tiddeman, B. H., 87, 263, 270
Till, 262
Time, geological, 294-296
Toarcian series, 227, 229
Topley, W., 130, 239
Torridonian beds, 135-137
Tremadoc slates, 152, 155, 162, 163
Triassic fauna and flora, 223-225
Triassic system, 218-225;
ammonite zones of, 225
Trinucleus fauna, 165
Tullberg, S. A., 162
Turonian series, 236
Unconformity, 60, 78, 98
Underclays, 197
Uniformitarianism, 287-292
Uriconian rocks, 138
Ussher, W. A. E., 183
Valentian beds, 175
Verneuil, E. P. de, 161
Volcanic rocks, Cambrian, 155;
Carboniferous, 199;
Devonian, 184, 186;
Eocene, 246, 247;
Ordovician, 165-170;
Precambrian, 146
Vulcanicity, 289
Waagen, W., 213, 214
Walcott, C. D., 144, 158, 160, 161, 173
Wallace, A. R., 124, 235, 240, 281, 295
Ward, J. C., 87, 88, 263, 295
Warming, E., 115
Watts, W. W., 142, 168, 178
Wealden beds, 236, 237
Webster, T., 18
Weissliegende, 214
Wenlock limestone, 175, 176
Wenlock series, 174-177
Wenlock shale, 175-177
Werfener Schichten, 225
Werner, A. G., 12
Weybourne crag, 256
Whewell, W., 50
Whidbourne, G. F., 91
White Jura, 226
Whitehaven sandstone, 202
Whitehurst, J., 11, 12
Wiman, C., 46
Wood, S. V., 250, 259
Woodward, H., 191
Woodward, H. B., 68, 130, 131
Woodward, J., 8-10
Woodward, S. P., 108, 111
Woolhope limestone, 175
Woolwich beds, 244
Wright, G. F., 263
Yoredale series, 192
Zanclean series, 256
Zechstein, 209
Zone, fossil, 67;
ammonite, 225, 237;
graptolite, 69
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H. K. LEWIS, 136, GOWER STREET, W.C.
_Medical Publisher and Bookseller._
Transcriber's Note
Any obsolete or alternate spelling and grammar was retained. All
obvious typographical errors were corrected. Although hyphenation of
words has been standardized to the most prevalent occurrence, the six
occurrences of fresh-water were not converted to freshwater (30
occurrences) due to usage. Corrected spellings: Godwin-Austen (p. 20);
Whidbourne (p. 191); and Ichthyopterygia (p. 223).