ACCOUNT OF THE GROWTH AND PROGRESS OF STRATIGRAPHICAL GEOLOGY.
The history of the growth of a science is not always treated as an
essential part of our knowledge of that science, and many text-books
barely allude to the past progress of the science with which they
deal. The importance of a review of past progress has, however,
attracted the attention of many geologists, and Sir Charles Lyell, in
his _Principles of Geology_, gave prominence to an historical sketch
of the rise and progress of the science. Historical studies of this
nature have more than an academic value; the very errors made by men
in past times are useful as warnings to prevent those of the present
day from going astray; the lines along which a science has progressed
in the past may often be used as guides to indicate how work is to be
conducted in the future; but perhaps the greatest lesson which is
taught by a careful consideration of the rise and progress of a study
is one which has a moral value, for he who pays attention to the
growth of his science in past times, gains a reverence for the old
masters, and at the same time learns that a slavish regard for
authority is a dangerous thing. This is a lesson which is of the
utmost importance to the student who wishes to advance his science,
and will prevent him from paying too little attention to the work of
those who have gone before him, whilst it will enable him to perceive
that as great men have fallen into error through not having sufficient
data at their disposal, he need not be unduly troubled should he find
that conclusions which he has lawfully attained after consideration of
evidence unknown to his predecessors clash with those which they
adopted. Want of this historic knowledge has no doubt caused many
workers to waste their time on work which has already been performed,
but it has also led others to withhold important conclusions from
their fellow-workers because they were supposed to be heterodox. In an
uncertain science like geology one of the great difficulties is to
keep an even balance between contempt and undue respect for authority,
and assuredly a scientific study of the past history of a science will
do much to enable a student to attain this end. It will be useful,
therefore, at this point to give a brief account of the rise and
progress of the study of stratigraphical geology, so far as that can
be done without entering into technical details, at the same time
recommending the student to survey the progress of this branch of our
science for himself, after he has mastered the principles of the
subject, and such details as are the property of all who have studied
the science from the various text-books written for advanced students.
William Smith, the 'Father of English Geology,' is rightly regarded as
the founder of stratigraphical geology on a true scientific basis, but
like all great discoverers, his work was foreshadowed by others,
though so dimly, that this does not and cannot detract from his fame.
It is desirable, however, to begin our historical review at a time
somewhat further back than that at which Smith gave to the world his
epoch-making map and memoirs.
Before the eighteenth century, stratigraphical geology cannot be said
to have existed as a branch of science--the way had not been prepared
for it. Data had been accumulated which would have been invaluable if
at the disposal of open-minded philosophers, but with few exceptions
prejudice prevented the truth from becoming known. There were two
great stumbling-blocks to the establishment of a definite system of
stratigraphical geology by the writers of the Middle Ages, firstly,
the contention that fossils were not the relics of organisms, and,
secondly, when it was conceded that they represented portions of
organisms which had once existed, the assertion that they had reached
their present positions out of reach of the sea during the Noachian
Deluge. For full details concerning the mischievous effects of these
tenets upon the science the reader is referred to the luminous sketch
of the growth of geology in the first four chapters of Sir Charles
Lyell's _Principles of Geology_.
The disposition of rocks in strata, and the occurrence of different
fossils in different strata, was known to Woodward when he published
his _Essay toward a Natural History of the Earth_ in 1695, and the
valuable collections made by Woodward and now deposited in the
Woodwardian Museum at Cambridge, show how fully he appreciated the
importance of these facts, though he formed very erroneous conclusions
from them, owing to the manner in which he drew upon his imagination
when facts failed him, maintaining that fossils were deposited in the
strata according to their gravity, the heaviest sinking first, and the
lightest last, during the time of the universal deluge. The following
extracts from Part II. of Woodward's book, show the position in which
our knowledge of the strata stood at the end of the seventeenth
century: "The Matter, subsiding ..., formed the _Strata_ of Stone, of
Marble, of Cole, of Earth, and the rest; of which Strata, lying one
upon another, the Terrestrial Globe, or at least as much of it as is
ever displayed to view, doth mainly consist.... The Shells of those
Cockles, Escalops, Perewinkles, and the rest, which have a greater
degree of Gravity, were enclosed and lodged in the _Strata_ of Stone,
Marble, and the heavier kinds of Terrestrial Matter: the lighter
Shells not sinking down till afterwards, and so falling amongst the
lighter Matter, such as Chalk, and the like ... accordingly we now
find the lighter kinds of Shells, such as those of the _Echini_, and
the like, very plentifully in Chalk.... Humane Bodies, the Bodies of
Quadrupeds, and other Land-Animals, of Birds, of Fishes, both of the
Cartilaginous, the Squamose, and Crustaceous kinds; the Bones, Teeth,
Horns, and other parts of Beasts, and of Fishes: the Shells of
Land-Snails: and the Shells of those River and Sea Shell-Fish that
were lighter than Chalk &c. Trees, Shrubs, and all other Vegetables,
and the Seeds of them: and that peculiar Terrestrial Matter whereof
these consist, and out of which they are all formed, ... were not
precipitated till the last, and so lay above all the former,
constituting the supreme or outmost _Stratum_ of the Globe.... The
said _Strata_, whether of Stone, of Chalk, of Cole, of Earth, or
whatever other Matter they consisted of, lying thus each upon other,
were all originally parallel: ... they were plain, eaven, and
regular.... After some time the _Strata_ were broken, on all sides of
the Globe: ... they were dislocated, and their Situation varied, being
elevated in some places, and depressed in others ... the Agent, or
force, which effected this Disruption and Dislocation of the
_Strata_, was seated _within_ the Earth."
Woodward's writings no doubt exercised a direct influence on the
growth of our subject, but the indirect effects of his munificent
bequest to the University of Cambridge and his foundation of the Chair
of Geology in that University were even greater, for as will be
pointed out in its proper place, two of the occupants of that chair
played a considerable part in raising stratigraphical geology to the
position which it now occupies.
The discoveries which were made after the publication of Woodward's
book and before the appearance of the map and writings of William
Smith are given in the memoir of the latter author, written by his
nephew, who formerly occupied the Chair of Geology at Oxford[1]. It
would appear that the fact that "the strata, considered as definitely
extended masses, were arranged one upon another in a certain _settled
order_ or _series_" was first published by John Strachey in the
_Philosophical Transactions_ for 1719 and 1725. "In a section he
represents, in their true order, chalk, oolites, lias, red marls and
coal, and the metalliferous rocks" of Somersetshire, but confines his
attention to the rocks of a limited district.
[Footnote 1: _Memoirs of William Smith, LL.D._ By J. Phillips, F.R.S.,
F.G.S. 1844.]
The Rev. John Michell published in the _Philosophical Transactions_
for 1760 an "Essay on the Cause and Phænomena of Earthquakes," but
Prof. Phillips gives proofs that Michell, who in 1762 became
Woodwardian Professor, had before 1788 discovered (what he never
published) the first approximate succession of the Mesozoic rocks, in
the district extending from Yorkshire to the country about Cambridge.
Michell's account was discovered written by Smeaton on the back of a
letter dated 1788. The following is the succession as quoted in
Phillips' memoir (p. 136):
Yards of thickness.
"Chalk 120
Golt 50
Sand of Bedfordshire 10 to 20
Northamptonshire lime and Portland
lime, lying in several strata 100
Lyas strata 78 to 100
Sand of Newark about 30
Red Clay of Tuxford, and several 100
Sherwood Forest pebbles and gravel 50 unequal
Very fine white sand uncertain
Roche Abbey and Brotherton limes 100
Coal strata of Yorkshire --"
The order of succession of the Cretaceous, Jurassic, Triassic and
Permian beds will be readily recognised as indicated in this section,
though the discovery of the detailed succession of the Jurassic rocks
was reserved for Smith.
In the year 1778, John Whitehurst published _An Inquiry into the
Original State and Formation of the Earth_, containing an Appendix in
which the general succession of the strata of Derbyshire is noted. The
main points of interest are that the author clearly recognised the
'toad-stones' of Derbyshire as igneous rocks, "as much a _lava_ as
that which flows from Hecla, Vesuvius, or Ætna," though he believed
that they were intrusive and not contemporaneous, and he also
foreshadows the distinction between the solid strata and the
superficial deposits,--"we may conclude," he says, "that all beds of
sand and gravel are assemblages of adventitious bodies and not
original _strata_: therefore wherever sand or gravel form the surface
of the earth, they conceal the original _strata_ from our observation,
and deprive us of the advantages of judging, whether coal or limestone
are contained in the lower regions of the earth, and more especially
in flat countries where the _strata_ do not basset."
Werner, who was born in 1750, exercised more influence by his teaching
than by his writings. His ideas of stratigraphical geology were
somewhat vitiated by his theoretical views concerning the deposition
of sediment from a universal ocean, in a definite order, beginning
with granite, followed by gneiss, schists, serpentines, porphyries and
traps, and lastly ordinary sediments. He recognised and taught that
these rocks had a definite order "in which the remains of living
bodies are successively accumulated, in an order not less determinate
than that of the rocks which contain them[2]." The limited value of
Werner's stratigraphical teaching is accounted for by Lyell, who
remarks that "Werner had not travelled to distant countries; he had
merely explored a small portion of Germany, and conceived and
persuaded others to believe that the whole surface of our planet, and
all the mountain-chains in the world, were made after the model of his
own province," and the author of the _Principles_ justly calls
attention to the great importance of travel to the geologist. Those
who cannot travel extensively should at any rate pay special attention
to the works published upon districts other than their own, and even
at the present time, the writings of some British workers are apt to
be marked by some of that 'insularity' which our neighbours regard as
a national characteristic.
[Footnote 2: Cuvier's _Eloge_.]
It is now time to turn directly to the work of William Smith, who, of
all men, exercised the most profound influence upon the study of
stratigraphical geology and may indeed be regarded as the true founder
of that branch of the science. The memoir of his life which was
before mentioned is all too short to illustrate the methods of work
which he followed, but in it we can trace his success to three
things:--firstly, his 'eye for a country,' to use a phrase which is
thoroughly understood by practical geologists, though it is hard
to explain to others, inasmuch as it epitomises a number of
qualifications of which the most important are, a ready recognition of
the main geological features from some coign of vantage, an intuitive
perception of what to note and what to neglect, and the power of
storing up acquired information in the mind rather than the note-book,
so that one may use it almost unconsciously for future work; secondly,
ability to draw conclusions from his observations, and thirdly, and
perhaps most important of all in its ultimate results, a facility for
checking these conclusions by means of further observations, and
dropping those which were clearly erroneous, whilst extracting the
truth from those which contained a germ of truth mixed with error.
Besides writers referred to above "some foreign writers, in particular
Scilla and Rouelle, appear to have made very just comparisons of the
natural associations of fossil shells, corals, &c. in the earth, with
the groups of similar objects as they are found in the sea, and thus
to have produced new proofs of the organic origin of these fossil
bodies; but they give no sign of any knowledge of the _limitation of
particular tribes of organic remains to particular strata_, of the
_successive existence of different groups of organization_, on
_successive beds of the antient sea_. Mr Smith's claim to this happy
and fertile induction is clear and unquestionable[3]." We get a clue
to the manner in which he arrived at his view in the following
passage[4]:--"Accustomed to view the surfaces of the several strata
which are met with near Bath uncovered in large breadths at once, Mr
Smith saw with the distinctness of certainty, that 'each stratum had
been in succession the bed of the sea'; finding in several of these
strata abundance of the exuviae of marine animals, he concluded that
these animals had lived and died during the period of time which
elapsed between the formation of the stratum below and the stratum
above, at or near the places where now they are imbedded; and
observing that in the successively-deposited strata the organic
remains were of different forms and structures--Gryphites in the lias,
Trigoniæ in the inferior oolite, hooked oysters in the fuller's
earth,--and finding these facts repeated in other districts, he
inferred that each of the separate periods occupied in the formation
of the strata was accompanied by a peculiar series of the forms of
organic life, that these forms characterized those periods, and that
the different strata could be identified in different localities and
otherwise doubtful cases by peculiar imbedded organic remains[5]."
[Footnote 3: _Memoir of William Smith_, p. 142.]
[Footnote 4: _Ibid._ p. 141.]
[Footnote 5: The work of Smith which directly bears upon the
establishment of the law of identification of strata by included
organisms is published in two treatises, entitled:--
(i) _Strata identified by Organized Fossils_, 4to. (intended to
comprise seven parts, of which four only were published), commenced in
1816.
(ii) _A Stratigraphical System of Organized Fossils_, compiled from
the original Geological Collection deposited in the British Museum.
4to. 1817.]
William Smith seems to have recognised intuitively the truth of a law
which was but dimly understood before his time,--the law of
superposition, which may be thus stated: "of any two strata, the one
which was originally the lower, is the older." This may appear
self-evident but it was certainly not so. As the result of this
recognition he established the second great stratigraphical law, with
which his name will ever be linked, that strata are identifiable by
their included organisms.
Before Smith's time, geological maps were lithological rather than
stratigraphical, they represented the different kinds of rocks seen
upon the surface without regard to their age; since Smith
revolutionised geology, the maps of a country composed largely of
stratified rocks are essentially stratigraphical, but partly no doubt
on account of adherence to old custom, partly on economic grounds, the
majority of our stratigraphical maps are lithological rather than
palæontological, that is the subdivisions of the strata represented
upon the map are chosen rather on account of lithological
peculiarities than because of the variations in their enclosed
organisms. It is hardly likely that Government surveys will be allowed
to publish palæontological maps, which will be almost exclusively of
theoretical interest, and it remains for zealous private individuals
to accomplish the production of such maps. When they are produced, a
comparison of stratigraphical maps founded on lithological and
palæontological considerations will furnish results of extreme
scientific interest.
Turning now from Smith's contributions to the science as a whole, we
may now consider what he did for British geology. His geological map
was published in 1815 and was described as follows:--"A Geological Map
of England and Wales, with part of Scotland; exhibiting the
Collieries, Mines, and Canals, the Marshes and Fen Lands originally
overflowed by the Sea, and the varieties of Soil, according to the
variations of the Substrata; illustrated by the most descriptive Names
of Places and of Local Districts; showing also the Rivers, Sites of
Parks, and principal Seats of the Nobility and Gentry, and the
opposite Coast of France. By William Smith, Mineral Surveyor." The map
was originally on the scale of five miles to an inch. In 1819 a
reduced map was published, and in later years a series of county maps.
He also published several geological sections, including one (in 1819)
showing the strata from London to Snowdon.
The student should compare Smith's map of the strata with one
published in modern times in order to see how accurate was Smith's
delineation of the outcrop of the later deposits of our island.
The following table, taken from Phillips' memoir, p. 146, is also of
interest as showing the development of Smith's work and the
completeness of his classification in his later years, and as
illustrating how much we are indebted to Smith for our present
nomenclature, so much so that as Prof. Sedgwick remarked when
presenting the first Wollaston Medal of the Geological Society to
Smith, "If in the pride of our present strength, we were disposed to
forget our origin, our very speech would bewray us: for we use the
language which he taught us in the infancy of our science. If we, by
our united efforts, are chiselling the ornaments and slowly raising up
the pinnacles of one of the temples of nature, it was he who gave the
plan, and laid the foundations, and erected a portion of the solid
walls by the unassisted labour of his hands."[6]
[Footnote 6: The reader may consult an interesting paper by Professor
Judd, on "William Smith's Manuscript Maps," _Geological Magazine_,
Decade IV. vol. IV. (1897) p. 439.]
Comparative View of the Names and Succession of the Strata.
--------------------+-------------------------+--------------------------
| | Improved table drawn up
Table drawn up | Table accompanying the | in 1815 and 1816 after
in 1799. | map, drawn up in 1812. | the first copies of the
| | map had been issued.
--------------------+-------------------------+--------------------------
| London Clay | 1 London Clay
| Clay or Brick-earth | 2 Sand
| | 3 Crag
| Sand or light loam | 4 Sand
1 Chalk | Chalk | 5 Chalk { Upper
| | { Lower
2 Sand | Green Sand | 6 Green Sand
| Blue Marl | 7 Brick Earth
| Purbeck Stone, Kentish {| 8 Sand
| Rag and Limestone {| 9 Portland Rock
| of the vales {| 10 Sand
| of Pickering and {| 11 Oaktree Clay
| Aylesbury, {| 12 Coral Rag and Pisolite
| Iron Sand and Carstone {| 13 Sand
3 Clay | Dark Blue Shale | 14 Clunch Clay and Shale
| | 15 Kelloway's Stone
| Cornbrash | 16 Cornbrash
4 Sand and Stone | | 17 Sand and Sandstone
5 Clay | |
6 Forest Marble | Forest Marble Rock | 18 Forest Marble
| | 19 Clay over Upper
| | Oolite
7 Freestone | Great Oolite Rock | 20 Upper Oolite
8 Blue Clay }| |
9 Yellow Clay }| |
10 Fuller's Earth }| | 21 Fuller's Earth and
}| | Rock
11 Bastard ditto }| |
and Sundries }| |
12 Freestone | Under Oolite | 22 Under Oolite
13 Sand | | 23 Sand
| | 24 Marlstone
14 Marl Blue | Blue Marl | 25 Blue Marl
15 Blue Lias | Blue Lias | 26 Blue Lias
16 White Lias | White Lias | 27 White Lias
17 Marlstone, Indigo| |
and Black Marls | |
18 Red Ground | Red Marl and Gypsum | 28 Red Marl
19 Millstone | Magnesian Limestone | 29 Redland Limestone
| Soft Sandstone |
20 Pennant Street }| |
21 Grays }| Coal Districts | 30 Coal Measures
22 Cliff }| |
23 Coal }| |
| Derbyshire Limestone | 31 Mountain Limestone
| Red and Dunstone | 32 Red Rhab and Dunstone
| Killas or Slate | 33 Killas
| Granite, Sienite and | 34 Granite, Sienite and
| Gneiss | Gneiss
--------------------+-------------------------+--------------------------
The above table contains a very complete classification of the British
Mesozoic rocks, one of the Tertiary strata which is less complete, and
a preliminary division of the Palæozoic rocks into Permian (Redland
Limestone), Carboniferous (Coal Measures and Mountain Limestone),
Devonian (Red Rhab and Dunstone) and Lower Palæozoic (Killas).
Since Smith's time the main work which has been done in classification
is a fuller elucidation of the sequence of the Tertiary and Palæozoic
Rocks, and this we may now consider.
The Mesozoic rocks are developed in Britain under circumstances which
render the application of the test of superposition comparatively
simple, for the various subdivisions crop out on the surface over long
distances, and the stratification is not greatly disturbed. With the
Tertiary and Palæozoic Rocks it is otherwise, for some members of the
former are found in isolated patches, whilst the latter have usually
been much disturbed after their formation.
Commencing with the Tertiary deposits we may note that "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.... 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 fossil shells were specifically
identical[7]." It is to Lyell that we owe the establishment of a
satisfactory classification of the Tertiary deposits which is the
basis of later classifications. Recognising the difficulty of
applying the ordinary test of superposition to deposits so scattered
as are those of Tertiary age in north-west Europe, he in 1830,
assisted by G. P. Deshayes, proposed a classification based on the
percentage of recent mollusca in the various deposits. It may be
noted, that although this method was sufficient for the purpose, it
has been practically superseded, as the result of increase of our
knowledge of the Tertiary faunas, by the more general method of
identifying the various divisions by their actual fossils without
reference to the number of living forms contained amongst them. The
further study of the British Tertiary rocks was largely carried on by
Joseph Prestwich, formerly Professor of Geology in the University of
Oxford.
[Footnote 7: Lyell, _Students' Elements of Geology_. 2nd Edition, p.
118.]
Amongst the Palæozoic rocks, it has been seen that the Permian,
Carboniferous and some of the Devonian beds were recognised as
distinct by Smith, though a large number of deposits now known to
belong to the last named were thrown in with other rocks as 'killas.'
The Devonian system was established and the name given to it in 1838
by Sedgwick and Murchison, largely owing to the palæontological
researches of Lonsdale. An attempt was subsequently made to abolish
the system, but the detailed palæontological studies of R. Etheridge
finally placed it upon a secure basis. The establishment of the
Devonian system cleared the way for the right understanding of the
Lower Palæozoic rocks, which Sedgwick and Murchison had commenced to
study before the actual establishment of the Devonian system, and to
these workers belongs the credit of practically completing what was
begun by William Smith, namely, the establishment of the Geological
Sequence of the British strata. The controversy which unfortunately
marked the early years of the study of the British Lower Palæozoic
Rocks is well-nigh forgotten, and in the future the names of Sedgwick
and Murchison will be handed down together, in the manner which is
most fitting.
Our account of the growth of British Stratigraphical Geology is not
yet complete. In 1854, Sir William Logan applied the term Laurentian
to a group of rocks discovered in Canada, which occurred beneath the
Lower Palæozoic Rocks. Murchison shortly afterwards claimed certain
rocks in N.W. Scotland as being of generally similar age, and since
then a number of geologists, most of whom are still living, have
proved the occurrence of several large subdivisions of rocks in
Britain, each of which is of pre-Palæozoic age.
The above is a brief description of the growth of our knowledge of the
order of succession of the strata which is the foundation of
Stratigraphical Geology. A sketch of the manner in which the knowledge
which has been obtained has been applied to the elucidation of the
earth's history of different times would require far more space than
can be devoted to it in a work like the present, but some idea of it
may be gained from a study of the later chapters of the book. It will
suffice here to remark, that to Godwin-Austen we owe the foundation of
what may be termed the physical branch of Palæo-physiography, which is
concerned with the restoration of the physical conditions of past
ages, while Cuvier and Darwin have exerted the most influence on the
study of Stratigraphical Palæontology.