quite abrupt and precipitous from the sea, similar marks of the
lowering of the sea, or the rising of the land, may be observed. On the
shores opposite to ours, the same appearances are remarked. The author
of the Lettre Critique to M. de Buffon, tells us, that he had found
the bottom of a bason at Dunkirk, which he had reason to think was dug
about 950 years ago, ten feet and a half above the present low water
mark, though it must have been originally under it. The bottom of this
bason is in the native chalk. From this, the same author concludes,
that the sea at Dunkirk lowers its level at the rate of an inch nearly
in seven years. The observation was made in 1762, (Lettre à M. le
Comte de Buffon, &c. p. 55.)[201]
[Footnote 201: In the county of Suffolk, near Wood Bridge, at the
distance of seven or eight miles from the sea, are the Crag-pits, in
which prodigious quantities of sea shells are discovered, many of them
perfect and quite solid, (Pennant's Arctic Zoology, Introd. p. 6.)
Lincolnshire affords various proofs of the same kind; but some other
circumstances in the appearance of that coast, just about to be taken
notice of, indicate changes of a more complicated nature.]
391. The shores of the Low Countries, and of Holland, have been often
instanced in proof of the same kind of changes, and it has been
supposed, that, independently of those artificial barriers which at
present exclude the waters of the ocean from overflowing a great part
of this tract, nature herself has brought it nearer to the surface
than it had formerly been. It is indeed certain, that those countries,
to a very great extent inland, have either been under the sea at some
period, by no means remote if compared with the great revolutions of
the globe, or that they are entirely alluvial, and of the same sort
with the Deltas formed at the mouths of rivers. The relative changes,
however, of the sea and land on this tract, have been differently
represented, and I am unwilling, on that account, to found any
argument on them.
392. If we proceed farther to the north, to the shores of the Baltic
for instance, we have undoubted evidence of a change of level in the
same direction as on our own shores. The level of this sea has been
represented as lowering at so great a rate as 40 inches in a century.
Celsius observed, that several rocks which are now above water,
were not long ago sunken rocks, and dangerous to navigators; and he
particularly took notice of one, which, in the year 1680, was on the
surface of the water, and in the year 1791 was 20-1/2 Swedish inches
above it. From an inscription near Aspô, in the lake Melar, which
communicates with the Baltic, engraved, as is supposed, about five
centuries ago, the level of the sea appears to have sunk in that time
no less than 13 Swedish feet.[202] All these facts, with many more
which it is unnecessary to enumerate, make the gradual depression,
not only of the Baltic, but of the whole northern ocean, a matter of
certainty.
[Footnote 202: Frisii Opera, tom. iii. p. 274.]
393. Supposing these changes of level between the sea and land to be
sufficiently ascertained, the supposition which at first occurs is,
that the motion has been in the sea rather than in the land, and that
the former has actually descended to a lower level. The imagination
naturally feels less difficulty in conceiving, that an unstable
fluid like the sea, which changes its level twice every day, has
undergone a permanent depression in its surface, than that the land,
the _terra firma_ itself, has admitted of an equal elevation. In all
this, however, we are guided much more by fancy than reason; for, in
order to depress or elevate the absolute level of the sea, by a given
quantity, in any one place, we must depress or elevate it by the same
quantity over the whole surface of the earth; whereas no such necessity
exists with respect to the elevation or depression of the land. To
make the sea subside 30 feet all round the coast of Great Britain, it
is necessary to displace a body of water 30 feet deep over the whole
surface of the ocean. The quantity of matter to be moved in that way is
incomparably greater than if the land itself were to be elevated; for
though it is nearly three times less in specific gravity, it is as much
greater in bulk, as the surface of the ocean is greater than that of
this island.
394. Besides, the sea cannot change its level, without a proportional
change in the solid bottom on which it rests. Though there be reason to
suppose that such changes in the bottom do actually take place, yet
they are probably much slower and more imperceptible than those which
we are here considering. It is evident, therefore, that the simplest
hypothesis for explaining those changes of level, is, that they proceed
from the motion, upwards or downwards, of the land itself, and not
from that of the sea. As no elevation or depression of the sea can
take place, but over the whole, its level cannot be affected by local
causes, and is probably as little subject to variation as any thing to
be met with on the surface of the globe.
395. Other observations, however, made on different shores from the
preceding, give greater certainty to this conclusion, and make it
clear, that the motion or change which we are now treating of is not to
be ascribed to the sea itself.
The observations just mentioned prove, that the level of the North
Sea is lower now than it was heretofore; but it appears, that in the
Mediterranean, the opposite takes place. Very accurate observations
made by MANFREDI, render it certain, that the superficies of the
Hadriatic was higher about the middle of the last century, than toward
the beginning of the Christian era.
Some repairs that were carrying on in the cathedral church of Ravenna,
in the year 1731, afforded him an opportunity of observing, that the
ancient, and probably original, pavement, was four feet and a half
below the present, and nearly a foot under the level of the sea at high
water.[203] Now, when the church was built, this cannot have been the
position of the pavement, relatively to the level of the sea, for it
would have subjected the floor to be under water twice in twenty-four
hours, and must have done so the more unavoidably, because at that time
(the beginning of the fifth century) the walls of Ravenna were washed
by the sea. The fact that this pavement is under the high-water mark,
by the quantity just mentioned, was ascertained by actual levelling.
This result was confirmed by similar facts, observed by ZENDRINI at
Venice.
[Footnote 203: Commentarii Academiæ Bononiensis, tom. ii. pars 1ma, p.
237, &c. and pars 2da, p. 1. &c.]
396. Manfredi himself attributes all this to the elevation of the
surface of the sea, and has entered into a long calculation to
ascertain at what rate that surface may be supposed to rise, on account
of the earth and sand brought down by the rivers, and spread out over
the bottom of the sea. But as the fact of the rise of the level of the
sea is not general, and as the contrary is observed in the north seas,
as already proved, this hypothesis will not explain the apparent rise
in the level of the Hadriatic.
397. Though a local subsidence, or settling of the ground, could hardly
account for this change, the pavement being perfect in its level, and
the walls of the cathedral without any shake, yet a subsidence that
has extended to a great tract, as to the whole of Italy, if the mass
moved has continued parallel to itself, and changed its place slowly,
will agree very well with the appearances. The facts here stated are
also the more deserving of attention, that about Ravenna, the land, at
the same time that it has sunk in its level, has extended its surface,
and has encroached on the sea. Since the time of AUGUSTUS, the line
of the coast has been carried farther out by about three miles.[204]
This last is the undoubted effect of the degradation of the land by the
rivers; and here we have very clear evidence of the forces, both under
and above the surface, producing their respective effects at the same
time, so that while the surface is raised by earth brought down by the
rivers, every given point in the ground is depressed and let down to a
lower level.[205]
[Footnote 204: Manfredi, _ibid._]
[Footnote 205: On the coast of Dalmatia also, the rising of the level
of the sea has been remarked, particularly at the ruins of Diocletian's
palace of Spalatro.]
398. On the southern coast of Italy similar facts have been observed.
BREISLAC, in his _Topographia Fisica della Campagnia di Roma_,[206]
from certain appearances in the Gulfs of Baja and Naples, concludes,
that at the beginning of the Christian era, the level of the sea was
lower on that part of the coast than it is now. The facts which he
mentions are the following: _1mo_, The remains of an ancient road are
now to be seen in the Gulf of Baja at a considerable distance from
the land. _2do_, Some ancient buildings belonging to Porto Giulio are
at present covered by the sea. _3tio_, Ten columns of granite at the
foot of Monte Nuovo, which appear to have belonged to the Temple of
the Nymphs, are also nearly covered by the sea. _4to_, The pavement of
the Temple of Serapis is now somewhat lower than the high water mark,
though it cannot be supposed that this edifice when built was exposed
to the inconvenience of having its floor frequently under water. _5to_,
The ruins of a palace, built by Tiberius in the island of Caprea, are
now entirely covered by the sea.
[Footnote 206: Cap. vi. p. 300.]
Thus, it appears that the level of the sea is sinking in the more
northern latitudes, and rising in the Mediterranean, and it is evident
that this cannot happen by the motion of the sea itself. The parts
of the ocean all communicating with one another, cannot rise in one
place and fall in another; but, in order to maintain a level surface,
must rise equally or fall equally over the whole of its extent. If,
therefore, we place any confidence in the preceding observations, and
they are certainly liable to no objection, either from their own nature
or the character of the observers, we must consider it as demonstrated,
that the relative change of level has proceeded from the elevation or
depression of the land itself. This agrees well with the preceding
theory, which holds, that our continents are subject to be acted upon
by the expansive forces of the mineral regions; that by these forces
they have been actually raised up, and are sustained by them in their
present situation.
399. According to some other facts stated by the same ingenious
author, it appears, that on the coast of Italy the progress of the
sea in ascending, or of the land in descending, has not been uniform
during the period above mentioned, but that different oscillations
have taken place; so that, from about the beginning of the Christian
era, till some time in the middle ages, the sea rose to be sixteen
feet higher than at present, from which height it has descended till
it became lower than it is now, and from that state of depression it
is now rising again. Breislac infers this from two facts, which he
combines very ingeniously with the preceding, viz. the remains of some
ancient buildings, at the foot of Monte Nuovo, five or six feet above
the present level of the sea, in which are found the shells of some
of those little marine animals that eat into stone: And again, the
marble columns of the temple of Serapis, which are also perforated
by pholades, to the height of sixteen feet above the ground. All
these changes Breislac ascribes to the motion of the sea itself; a
supposition which, as we have seen, cannot possibly be admitted, since
nothing can permanently affect the level of the sea in one place, which
does not affect it in all places whatsoever.
400. Appearances, which indicate such alternations as have just been
mentioned in the level of the sea, are to be met with on some other
coasts. In England, on the coast of Lincolnshire, the remains of a
forest have been observed, which are now entirely covered by the
sea.[207] The submarine stratum which contains the remains of this
forest, can be traced into the country to a great distance, and is
found throughout all the fens of Lincolnshire. The stratum itself is
about four feet thick; it is covered in some places by a bed of clay
sixteen feet thick, and under it for twenty feet more is a bed of soft
mud, like the scourings of a ditch, mixed with shells and silt.
[Footnote 207: Phil. Trans. 1799, p. 145.]
Here then we have a stratum which must have been once uppermost on the
surface of the dry land, though one part of it is now immersed under
the sea, and another covered with earth, to the depth of sixteen feet.
A change of level in the sea itself will not explain these appearances:
they can only be explained by supposing the whole tract of land to
have subsided, which is the hypothesis adopted by the author of the
description in the Transactions, M. CORRIA DE SERRA; the subsidence,
however, is not here understood to arise from the mere yielding of
some of the strata immediately underneath, but is conceived to be a
part of that geological system of alternate depression and elevation
of the surface, which probably extends to the whole mineral kingdom.
To reconcile all the different facts, I should be tempted to think,
that the forest which once covered Lincolnshire, was immersed under the
sea by the subsidence of the land to a great depth, and at a period
considerably remote; that when so immersed, it was covered over with
the bed of clay which now lies on it, by deposition from the sea, and
the washing down of earth from the land; that it has emerged from this
great depth till a part of it has become dry land; but that it is now
sinking again, if the tradition of the country deserves any credit,
that the part of it in the sea is deeper under water at present than
it was a few years ago. This might also serve to reconcile, in some
measure, the phenomena of this submarine forest with the appearances
which indicate an extension of the land on the coast of Lincolnshire.
Indeed the extension of the land is no direct proof, either of its own
elevation, or of the depression of the sea, as we may conclude from the
instance of Ravenna already mentioned.
401. We have concluded from the facts stated above, that the level of
the sea rises in the Mediterranean, and sinks in the more northern
latitudes; and thence some have suspected, that the level of the sea
had in general a tendency to rise towards the equator, and to sink
towards the poles. This is the notion of Frisi, as has been already
remarked, and he suggests, that this rise of the sea may be owing to a
slight acceleration in the earth's diurnal motion. But there are facts
which show, that between the tropics the relative level of the sea
and land has sunk, and is lower at present than it was at some former
period, probably not extremely remote. The opinion of Frisi, therefore,
is unsupported by observation, and, as has been already shown, cannot
be justified from theory.
Between the tropics, islands are formed from the mere accumulation
of coral; and it is the peculiarity of those regions, to produce
rocks that have not passed through the usual process of mineral
consolidation.[208] The islets, however, which are thus formed, must
have their bases laid on a solid rock, though perhaps at a great
depth; and it is not probable, that after they are once raised above
the surface of the sea, they can still rise farther, except by some
elevation of the rock which serves as their foundation.[209] Now,
at Palmerston island, which comprehends nine or ten low islets, that
may be reckoned the heads of a great reef of coral rock, Captain
Cook informs us of his having seen, "far beyond the reach of the
sea, even in the most violent storms, elevated coral rocks, which,
on examination, appeared to have been perforated in the same manner
that the rocks are that now compose the outer edge of the reef. This
evidently shows," he adds, "that the sea had formerly reached so far;
and some of these perforated rocks were almost in the centre of the
island."[210]
[Footnote 208: Dr Foster, in his Voyage round the World, (vol. ii. p.
146,) gives an instance in the South Sea Islands, where the surface of
the island, though entirely a coral rock, was raised forty feet above
the level of the sea.]
[Footnote 209: A very curious account of the formation of such islands
is given by A. Dalrymple, Esq., in the Philosophical Transitions, vol.
lvii. p. 394.]
[Footnote 210: Cook's Third Voyage, vol i. p. 221.]
The same excellent navigator, giving an account of the peninsula at
Cape Denbigh, remarks: "It appeared to me, that this peninsula must
have been an island in remote times; for there were marks of the sea
having flowed over the isthmus."
402. We are here touching on one of those subjects, where we feel much
the want of accurate and ancient observations, and where it is not from
the infancy, but the maturity of science that any thing approaching
to certainty can be looked for. The utmost that we can expect at
present, is an anticipation, which future ages must certainly modify
and correct. The best thing, in the mean time, that can be done for the
advancement of this branch of geological knowledge, is to ascertain
with exactness the relative level of the sea, and of such points upon
the land as can be distinctly marked, and pointed out to succeeding
ages. This is not so easy as it may at first appear. Where every object
changes, it is difficult to find a measure of change, or a fixed point
from which the computation may begin. The astronomers already feel
this inconvenience, and when they would refer their observations to
an immoveable plane, that shall preserve its position the same in all
ages, they meet with difficulties, which cannot be removed but by a
profound mathematical investigation.
In geology, we cannot hope to be delivered from this embarrassment in
the same manner; and we have no resource but to multiply observations
of the difference of level; to make them as exact as possible, and
to select points of comparison that have a chance of being long
distinguished. The improvements in barometrical measurements, which
give such facility to the determination of heights, along with so
considerable a degree of accuracy, will furnish an accumulation of
facts that must one day be of great value to the geologist.
NOTE XXII. § 123.
_Fossil Bones._
403. The remains of organized bodies, at present included in the solid
parts of the globe, may be divided into three classes. The first
consists of the shells, corals,-and even bodies of fish, and amphibious
animals, which are now converted into stone, and make integrant parts
of the solid rock. All these are parts of animals that existed _before
the formation of the present land_, or even of the rocks whereof it
consists. These remains have been already treated of, and the evidence
which they furnish must ever be regarded as of the utmost importance
in the theory of the earth. The second class consists of remains,
which, by the help of stalactitical concretions, are converted into
stone. These are the exuviæ of animals, which existed on the very same
continents on which we now dwell, and are no doubt the most ancient
among their inhabitants, of which any monument is preserved. In
comparison of the first class, they must, nevertheless, be considered
as of very modern origin.
404. The third class consists of the bones of animals found in the
loose earth or soil; these have not acquired a stony character, and
their nature appears to be but little changed, except by the progress
of decomposition and of mouldering into earth. No decided line can be
drawn between the antiquity of this and the preceding class, as there
may be between the preceding and the first. In some instances, the
objects of this third class may be coeval with those of the second; in
general, they must be accounted of later origin, as they are certainly
not preserved in a manner so well fitted for long continuance.
405. The animal remains of the second class, are generally found in
the neighbourhood of limestone strata, and are either enveloped or
penetrated by calcareous, or sometimes ferruginous matter. Of this
sort are the bones found in the rock of Gibraltar, and on the coast
of Dalmatia. The latter are peculiarly marked for their number, and
the extent of the country over which they are scattered, leaving it
doubtful whether they are the work of successive ages, or of some
sudden catastrophe that has assembled in one place, and overwhelmed
with immediate destruction, a vast multitude of the inhabitants of
the globe. These remains are found in greatest abundance in the
islands of Cherso and Osero ; end always in what the Abbé FORTIS calls
an _ocreo-stalactitic earth_. The bones are often in the state of
mere splinters, the broken and confused relics of various animals,
concreted with fragments of marble and lime, in clefts and chasms of
the strata.[211] Sometimes human bones are said to be found in these
confused masses.
[Footnote 211: Travels into Dalmatia, p. 449.]
406. A very remarkable collection of bones in this state is found
in the caves of Bayreuth in Franconia. Many of these belong, as is
inferred with great certainty from the structure of their teeth, to
a carnivorous animal of vast size, and having very little affinity
to any of those that are now known. The bones are found in different
states, some being without any stalactitical concretion, and having
the calcareous earth still united to the phosphoric acid, so that
they belong to the third, rather than the second, of the preceding
divisions. In others, the phosphoric acid has wholly disappeared, and
given place to the carbonic.
The number of these bones, accumulated in the same place, is matter of
astonishment, when it is considered, that the animals to which they
belonged were carnivorous, so that more than two can never have lived
in the same cavern at the same time. The caves of Bayreuth seem to have
been the den and the tomb of a whole dynasty of unknown monsters, that
issued from this central spot to devour the feebler inhabitants of the
woods, during a long succession of ages, before man had subdued the
earth, and freed it from all domination but his own.
407. The fossil bones of the second and third class, but chiefly of the
third, have now afforded matter of conjecture and discussion for more
than a century. The facts with respect to them are very numerous and
interesting, but can be considered here only very generally.
The remains of this kind, consist of the bones only of large animals,
so that they have generally been compared with those of the elephant,
the rhinoceros, the hippopotamus, or other animals of great size The
bones of smaller animals have also been found, but much more rarely
than the other. It is usually remarked, that the bones thus discovered
in the earth are larger than those of the similar living animals.
Another general fact concerning these remains, is, that they are found
in all countries whatsoever, but always in the loose or travelled
earth, and never in the genuine strata. Since the year 1696, when the
attention of the curious was called to this subject, by the skeleton
of an elephant dug up in Thuringia, and described by Tentzelius,[212]
there is hardly a country in Europe which has not afforded instances
of the same kind. Fossil bones, particularly grinders and tusks of
elephants, have been found in other places of Germany, in Poland,
France, Italy, Britain, Ireland, and even Iceland.[213] Two countries,
however, afford them in greater abundance by far than any other part of
the known world; namely, the plains of Siberia in the old continent,
and the flat grounds on the banks of the Ohio in the new.[214]
[Footnote 212: Phil. Trans. vol. xix. p. 757.]
[Footnote 213: A grinder of an elephant found in Iceland, is described
by _Bartholinus_, Acta Hafniens. vol. i. p. 83.]
[Footnote 214: The fossil bones on the Ohio are described in two papers
by Mr P. Collinson, Phil. Trans. vol. lvii. p. 464 and 468.]
408. When the bones in Siberia were first discovered, they were
supposed to belong to an animal that lived under ground, to which
they gave the name of the _mammouth_; and the credit bestowed on this
absurd fiction, is a proof of the strong desire which all men feel
of reconciling extraordinary appearances with the regular course of
nature. Much skill, however, in natural history was not required to
discover that many of the bones in question resembled those of the
elephant, particularly the grinders and the tusks of that animal.
Others resembled the bones of the rhinoceros; and a head of that kind,
having the hide preserved upon it, was found in Siberia, and is still
in the imperial cabinet at Petersburgh.
Pallas has described the fossil bones which he found in the museum at
Petersburgh, on his being appointed to the superintendence of it, and
enumerates, not only bones that belong, in his opinion, to the elephant
and rhinoceros, but others that belong to a kind of buffalo, very
different from any now known, and of a size vastly greater.[215] He has
also described, in another very curious memoir, the bones of the same
kind that he met with in his travels through the north-east parts of
Asia.
[Footnote 215: Novi Comment Petrop. tom. xiii. (1768,) p. 436, and tom.
xvii. p. 576, &c.]
The fossil bones found on the banks of the Ohio, resemble in many
things those of Siberia; like them they are contained in the soil or
alluvial earth, and never in the solid strata; like them too they are
no otherwise changed from their natural state, than by being sometimes
slightly calcined at the surface; they are also of great size, and in
great numbers, being probably the remains of several different species.
409. Two inquiries concerning these bones have excited the curiosity
of naturalists; first, to discover among the living tribes at present
inhabiting the earth, those to which the fossil remains may with the
greatest probability be referred; and, secondly, to find out the cause
why these remains exist in such quantities, in countries where the
animals to which they belong, whatever they be, are at present unknown.
The solution of the first of these questions, is much more within our
reach than the second, and at any rate must be first sought for.
On the authority of so eminent a naturalist as Pallas, the bones from
Siberia may safely be referred to the elephant, the rhinoceros, and
buffalo, as mentioned above, though perhaps to varieties of them with
which we are not now acquainted. With respect to the bones of North
America, the question is more doubtful, for they have this particular
circumstance attending them, viz. that along with the thighbones,
tusks, &c. which might be supposed to belong to the elephant, grinders
are always found of a structure and form entirely different from
the grinders of that animal.[216] Some naturalists, particularly M.
DAUBENTON, referred these grinders to the hippopotamus; but Dr W.
HUNTER appears to have proved, in a very satisfactory manner, that they
cannot have belonged to either of the animals just mentioned, but to a
_carnivorous_ animal of enormous size, the race of which, fortunately
for the present inhabitants of the earth, seems now to be entirely
extinct.[217] The foundation of Dr Hunter's opinion is, that in these
grinders the enamel is merely an external covering; whereas, in the
elephant, and other animals destined to live on vegetable food, the
enamel is intermixed with the substance of the tooth.[218]
[Footnote 216: See Mr Collinson's papers, above referred to. Phil.
Trans. vol. lvii.]
[Footnote 217: Phil. Trans. vol. lviii. p. 3, &c.]
[Footnote 218: A fossil grinder in the collection of JOHN MACGOWAN,
Esq. of Edinburgh, answers nearly to Mr Collinson's description, and is
very well represented by the figure which accompanies it. This grinder
weighs four pounds one-fourth avoirdupois; the circumference of the
_corona_ is eighteen inches; the coat of enamel is one-fourth of an
inch thick; there are five double teeth; in Mr Collinson's specimen
there are only four.]
410. Though this argument appears to be of considerable weight, yet
CAMPER, who was greatly skilled in comparative anatomy, and who had
studied this subject with particular attention, was of opinion, that
these grinders belong to a species of elephant. This opinion he states
in a letter to Pallas, who had found grinders and other bones of this
same animal, on the western declivity of the Ural mountains.[219]
Camper denies that the animal is carnivorous, because the _incisores_,
or canine teeth, are wanting; and he argues farther, from the weight of
the head, which may be inferred from the weight of the grinders, that
the neck must have been short, and the animal must have been furnished
with a _proboscis_. He afterwards abandoned the latter hypothesis, and
gave it as his opinion that the _incognitum_ was neither carnivorous,
nor a species of the elephant.[220]
[Footnote 219: Acta Acad. Petrop. tom. i. (1777,) pars posterior, p.
213, &c.]
[Footnote 220: _Ibid._ tom. ii. (1784,) p. 262.]
411. Nevertheless, CUVIER, in a _mémoire_ read before the National
Institute of Paris, maintains, that the fossil bones of the new
Continent, as well as most of those of the old, belong to certain
species of the elephant; of which, at least, two do not now exist, and
are only known from remains preserved in the ground. He distinguishes
them thus:[221]
[Footnote 221: Mémoires de l'Institut National, Sciences Physiques,
tom. ii. p. 19, &c.]
_Elephas mammonteus_,--_maxillâ obtusiore, lamellis molarium tenuibus,
rectis_.
_Elephas Americanus_,--_molarities multicuspidibus, lamellis post
detritionem quadric-lobatis_.
The latter species, which is meant to include the _animal incognitum_,
is said to have lived, not only in America, but in many parts of the
old Continent. Yet some late inquiries into the structure of the teeth
of graminivorous animals, and particularly of the elephant, make it
very improbable that the _incognitum_ has belonged to this genus.[222]
The grinders of the elephant have been found to consist of three
substances, enamel, bone, and what is called the _crusta petrosa_,
applied in layers, or folds contiguous to one another; and no vestige
of this structure appears in the grinders of the unknown animal of the
Ohio.[223] At the same time, Dr Hunter's assertion, that this animal
was carnivorous, is rendered doubtful, not only by the want of _canine_
teeth, but also from the resemblance between its grinders and those of
the wild boar, which Mr Home has observed to be considerable.[224] The
grinder of the boar is similar to that of the elephant, in the extent
of the masticating surface, but not at all in the internal structure;
and the same is true of the tooth of the _animal incognitum_, so that
a considerable probability is established, that it and the boar are of
the same genus, and both destined to live occasionally either on animal
or vegetable food.
[Footnote 222: See Mr Home's Observations on the Teeth of Graminivorous
Animals, Phil. Trans. 1799. Also, an Essay on the Structure of the
Teeth, by Dr Blake.]
[Footnote 223: In a paper inserted in the fourth volume of the American
Philosophical Transactions, an account is given of two different
grinders that are found at the Salt Licks near the Ohio. One of them
resembles the grinder of the elephant, and may have belonged to the
_Elephas Americanus_ of Cuvier; the other agrees pretty nearly with the
grinder of Dr Hunter's _animal incognitum_. The author of the paper
thinks that the _animal incognitum_ was not wholly carnivorous, as the
incisores, or canine teeth, are never found. At the Great Bone Lick,
bones of smaller animals, particularly of the buffalo kind, have been
discovered. The saline impregnation of the earth at these Licks must
no doubt have contributed to the preservation of the bones. Trans.
American Phil. Soc. vol. iv. (1799,) p. 510, &c.]
[Footnote 224: Observations on the Grinding Teeth of the wild boar and
_animal incognitum_. Phil. Trans. 1801, p. 319.]
412. Another _animal incognitum_ found in South America has been
described by Cuvier, and appears to be of a different genus from the
_incognitum_ of the North. Thus, if we include the two _incognita_ of
America, the _elephas mammonteus_, the unknown buffalo of Pallas, and
the great animal of Bayreuth, we have at least five distinct genera,
or species of the animal kingdom, which existed on our continents
formerly, but do not exist on them now. The number is probably much
greater: Pallas mentions fossil horns of a gazelle, of an unknown
species; and horns of deer are often found, that cannot be referred to
any species now existing. Those extinct races have been remarkable for
their size: some of the ancient elephants appear to have been three
times as large as any of the present.[225]
[Footnote 225: Camper, Nov. Acta Petrop. tom. ii. (1784) p. 257.]
413. The inhabitants of the globe, then, like all the other parts of
it, are subject to change. It is not only the individual that perishes,
but whole _species_, and even perhaps _genera_, are extinguished. It
is not unnatural to consider some part of this change as the operation
of man. The extension of his power would necessary subvert the balance
that had before been established between the inhabitants of the earth,
and the means of their subsistence. Some of the larger and fiercer
animals might indeed dispute with him, for a long time, the empire of
the globe; and it may have required the arm of a Hercules to subdue
the monsters which lurked in the caves of Bayreuth, or roamed on the
banks of the Ohio. But these, with others of the same character, were
at length exterminated: the more innocent species fled to a distance
from man; and being forced to retire into the most inaccessible parts,
where their food was scanty, and their migration checked, they may have
degenerated from, the size and strength of their ancestors, and some
species may have been entirely extinguished.
But besides this, a change in the animal kingdom seems to be a part of
the order of nature, and is visible in instances to which human power
cannot have extended. If we look to the most ancient inhabitants of the
globe, of which the remains are preserved in the strata themselves,
we find in the shells and corals of a former world hardly any that
resemble exactly those which exist in the present. The species, except
in a few instances, ate the same, but subject to great varieties. The
vegetable impressions on slate, and other argillaceous stones, can
seldom be exactly recognised; and even the insects included in amber
are different from those of the countries in which the amber is found.
414. Supposing, then, the changes which have taken place in the
qualities and habits of the animal creation, to be as great as those
in their structure and external form, we can have no reason to wonder
if it should appear that some have formerly dwelt in countries from
which the similar races are now entirely banished. The power of living
in a different climate, of enduring greater degrees of cold or of
heat, or of subsisting on different kinds of food, may very well have
accompanied the other changes. Though one species of elephant may
now be confined to the southern parts of Asia, another may have been
able to endure the severer climates of the north; and the same may
be true of the buffalo or the rhinoceros. In all this no physical
impossibility is involved; though whether it is a probable solution of
the difficulty concerning the origin of these animal remains, can only
be judged of from other circumstances.
415. If we consider attentively the facts that respect the Siberian
fossil bones, there will appear insurmountable objections to every
theory that supposes them to be exotic, and to have been brought into
their present situation from a distant country.
The extent of the tract through which these bones are scattered, is a
circumstance truly wonderful. Pallas assures us,[226] that there is not
a river of considerable size in all the north of Asia, from the Tanais,
which runs into the Black Sea, to the Anadyr, which falls into the Gulf
of Kamtchatka, in the sides or bottom of which bones of elephants and
other large animals have not been found. This is especially the case
where the rivers run in plains through gravel, sand, clay, &c.; among
the mountains, the bones are rarely discovered. The extent of the tract
just mentioned exceeds four thousand miles; and how the bones could
be distributed over all that extent, by any means but by the animals
having lived there, it seems impossible to conceive. No torrent nor
inundation could have produced this effect, nor could the bones brought
in that way have been laid together so as to form complete skeletons.
[Footnote 226: De Reliquiis Animalium exoticorum, per Asiam Borealem
repertis.--"Nov. Comment Petrop. tom. xvii. (1772,) p. 576.]
416. One fact recorded by the same author, seems calculated to remove
all uncertainty. It is that of the carcase of a rhinoceros, almost
entire, and covered with the hide, found in the earth in the banks of
the river Wilui, which falls into the Lena below Jakutsk.[227] Some of
the muscles and tendons were actually adhering to the head when Pallas
received it. The head, after being dried in an oven, is still preserved
in the museum at Petersburgh. The preservation of the skin and muscles
of this natural mummy, as Pallas calls it, was no doubt brought
about by its being buried in earth that was in a state of perpetual
congelation; for the place is in the parallel of 64°, where the ground
is never thawed but to a very small depth below the surface.
[Footnote 227: Pallas _ubi supra_, p. 586. Also, Voyages de Pallas,
tom. iv. p. 131.]
But by what means can we account for the carcase of a rhinoceros being
buried in the earth, on the confines of the polar circle? Shall we
ascribe it to some immense torrent, which, sweeping across the deserts
of Tartary, and the mountains of Altai, transported the productions of
India to the plains of Siberia, and interred in the mud of the Lena
the animals that had fed on the banks of the Barampooter or the Ganges?
Were all other objections to so extraordinary a supposition removed,
the preservation of the hide and muscles of a dead animal, and the
adhesion of the parts, while it was dragged for 2000 miles over some
of the highest and most rugged mountains in the world, is too absurd
to be for a moment admitted. Or shall we suppose that this carcase has
been floated in by an inundation of the sea, from some tropical country
now swallowed up, and of which the numerous islands of the Indian
Archipelago are the remains? The heat of a tropical climate, and the
putrescence naturally arising from it, would soon, independently of all
other accidents, have stripped the bones of their covering. Indeed this
_instantia singularis_, as in every sense it may properly be called,
seems calculated for the express purpose of excluding every hypothesis
but one from being employed to explain the origin of fossil bones.
It not only excludes the two which have just been mentioned, but it
excludes also that of Buffon, viz. that these bones are the remains of
animals which lived in Siberia, when the arctic regions enjoyed a fine
climate, and a temperature like that which southern Asia now possesses.
From the preservation of the flesh and hide of this rhinoceros, it is
plain, that when the body was buried in the earth, the climate was
much the same that it is now, and the cold sufficient to resist the
progress of putrefaction.
Pallas takes notice of the inconsistency of the state of this skeleton,
with the hypothesis of Buffon; but he does not observe that the
inconsistency is equally great between it and his own hypothesis, the
importation of the fossil bones by an inundation of the sea, and that
flesh or muscle must have been entirely consumed long before it could
be carried by the waves to the parallel of 64°, from any climate which
the rhinoceros at present inhabits.
417. The presence of petrified marine objects in places where some of
the fossil bones are found, is no proof that the latter have come from
the sea, though it is produced as such both by Pallas himself, and
afterwards by Kirwan. These marine bodies are the shells and corals
that have been parts of calcareous rocks, from which being detached
by the ordinary progress of disintegration, they are now contained in
the beds of sand or gravel where the animal remains are buried. They
have nothing in common with these remains; they are real stones, and
belong to another, and a far more remote epochs. Such objects being
found in the same place where the bones lie, argues only that the
strata in the higher grounds, from which the gravel has come, are
calcareous; and nothing can show in a stronger light the necessity of
distinguishing the different condition of fossil bodies, united by the
mere circumstance of contiguity, before we draw any inference as to
their having a common origin. If the marine remains were in the same
condition with the bones; if they were in no respect mineralized; then
the conclusion, that both had been imported by the sea, would have
great probability; but without that, their present union must be held
as casual, and can give no insight into the origin of either.
418. On the whole, therefore, no conclusion remains, but that these
bones have belonged to species of elephants, rhinoceros, &c. which
inhabited the very countries where their remains are now buried, and
which could endure the severity of the Siberian climate. The rhinoceros
of the Wilui certainly lived on the confines of the Polar Circle, and
was exposed to the same cold while alive, by which, when dead, its body
has been so long, and so curiously preserved.
These animals may also have lived occasionally farther to the south,
among the valleys between the great ranges of mountains that bound
Siberia on that side. Fossil bones are but rarely found in these
valleys, probably because they have been washed down from thence into
the plains. We must observe, too, that those animals may have migrated
with the seasons, and by that means avoided the rigorous winter of the
high latitudes. The dominion of man, by rendering such migration to
the larger animals difficult or impossible, must have greatly changed
the economy of all those tribes, and narrowed the circle of their
enjoyments and existence. The heaps in which the fossil bones appear to
be accumulated in particular places, especially in North America, have
a great appearance of being connected with the migrations of animals,
and the accidents that might bring multitudes of them into the same
spot.
What holds of Siberia and of North America, is applicable, _a
fortiori_, to all the other places where animal remains are found
in the same condition. Thus we are carried back to a time when many
larger species of animals, now entirely extinct, inhabited the earth,
and when varieties of those that are at present confined to particular
situations, were, either by the liberty of migration, or by their
natural constitution, accommodated to all the diversities of climate.
This period, though beyond the limits of ordinary chronology, is
posterior to the great revolutions on the earth's surface, and the
latest among geological epochs.
NOTE XXIII. § 128.
_Geology of_ KIRWAN _and_ DE LUC.
419. The two champions of the Neptunian system, who have distinguished
themselves most by their hostility to Dr HUTTON, are DE LUC and KIRWAN.
They have carried on their attack nearly on the same plan, and have
employed against their antagonist the weapons both of theology and
science. With a spirit as injurious to the dignity of religion, as to
the freedom of philosophical inquiry, they have disregarded a maxim
enforced by the authority of Bacon, and by all our experience of the
past; "_Tanto magis hæc vanitas inhibenda venit et coërcenda, quia,
ex divinorum et humanorum male-sana admixtione, non solum educitur
philosophia phantastica, sed etiam religio hæretica. Itaque salutare
admodum est, si mente sobriâ, fidei tantum dentur quæ fidei sunt_."[228]
[Footnote 228: The whole passage is deserving of attention, and
it seems as if the prophetic spirit of Bacon had addressed it to
the cosmologists of the present day. "_Pessima enim res errorem_
APOTHEOSIS, _et pro peste intellectús habenda est, si vanis accedat
veneratio. Huic autan vanitati nonnulli ex modernis summâ levitate ita
indulserunt, ut, in primo capitolo_ GENESEOS, _et aliis Scripturis
Sacris, philosophiam naturalem fundari conati sunt:_ Inter VIVA
quærentes MORTUA.--"Nov. Organum, lib. i. aphor. 65]
Proceeding, accordingly, in direct opposition to rules that, have never
yet been violated with impunity, and mistaking the true object of a
theory of the earth, they carry back their inquiries to a period prior
to the present series of causes and effects, where, having neither
experience nor analogy to direct them, they pretend to be guided by
a superior light. They would have us to consider their geological
speculations as a commentary on the text of MOSES; they endeavour to
explain the action of creative power, and, with indiscreet curiosity,
would tear off the veil which the hand of the prophet has so wisely
respected. But the veil cannot be torn off, and all that is behind it
must be to man as that which never has existed.
420. M. De Luc has nevertheless treated very diffusely of the history
of the solar system, previous to the establishment of the present laws
of nature, and has dwelt on it with great complacency, and singular
minuteness of detail. His tenth letter to LA METHERIE has the following
title:
"On the History of the Earth, from the time when that planet was
penetrated by _light_, till the appearance of the sun; a portion of
time which includes the origin of heat, and of the figure of the
earth; of its primeval strata, of the ancient sea, of our continents,
as the bottom of that sea, of the great chains of mountains, and of
vegetation."[229]
[Footnote 229: Journal de Physique, tom. 37. (1790,) partie 2de, p.
332. As I may not have done justice to this extraordinary title, it may
be right to present it in the original. "Sur l'Histoire de la TERRE,
depuis que cette planette fut penetrée de LUMIERE, jusqu'à l'apparition
du SOLEIL; espace de tems qui renferme les ORIGINES de la _chaleur_,
et de la _figure_ de notre globe; de ses _couches primordiales_, de
_l'ancienne mer_, de nos _continens_, comme fond de cette mer, de leurs
grandes chaînes de _montagnes_, et de la _vegetation_."]
I must confess that I am unacquainted with every thing of this letter
but the title; and could not easily be prevailed on to follow any man
who professedly goes out of nature in search of knowledge; who pretends
to give the history of our planetary system when there was no sun,
and to enumerate the events which took place between the existence of
that luminary, and the existence of light. The absurdity of such an
undertaking admits of no apology; and the smile which it might excite,
if addressed merely to the fancy, gives place to indignation when it
assumes the air of philosophic investigation.
421. It sets, however, in a strong light, the inconsistencies that
may be observed in the intellectual character of the same individual,
to consider that the author of this strange and inconsistent
reverie, is, nevertheless, an excellent observer, and well skilled in
experimental inquiries. It will hardly be believed that he who writes
the history of the earth before the formation of the sun, is versed
in the principles of inductive reasoning; and that he has added much
to the stock of geological knowledge, having observed accurately, and
described with great perspicuity and candour. His _Lettres Physiques_
are full of valuable and just observations, though accompanied with
reasonings that do not seem always entitled to the same praise; and
in another work he has succeeded where many men of genius had failed,
and has made considerable improvements in a branch of the mathematics,
without borrowing almost any assistance from the principles of that
science.[230]
[Footnote 230: Essai sur les Modifications de l'Atmosphere.]
422. Some of the same observations apply to Mr Kirwan. His Geological
Essays have also for their object to explain the first origin of
things; and to say that he has not succeeded, in an attempt where no
man ever can succeed, implies no reproach on the execution of his
work, whatever it may do on the design. We have indeed no criterion by
which the execution of it can be estimated: what would in any other
place be a blemish, may be here deserving of praise; and if the work
is full of confusion and perplexity, these are qualities inherent in
the subject which it is intended to describe. It were, no doubt, to
be wished, that after emerging into the regions of day, Mr Kirwan had
been as successful in copying the beauty and simplicity of nature, as
in representing the disorder and inconsistency of the chaotic mass.
But his cosmology is without unity in its principles, or consistency
in its parts; the causes introduced, are, for the most part, such as
will account for one set of appearances just as well as for another;
or, if any of them is likely to prove inadequate to the effect ascribed
to it, a new and arbitrary hypothesis is always ready to come to its
assistance. The information given is seldom exact: a multitude of facts
brought together, without the order and discussion essential to precise
knowledge; and an infinity of quotations, amassed without criticism or
comparison, afford proofs of extensive reading, but of the most hasty
and superficial inquiry. Thus we have seen passages from ULLOA and
FRISI, produced in support of opinions, which, when fairly stated, they
had the most direct tendency to overthrow.
423. In one respect, the geological writings of Kirwan are far inferior
to De Luc's: They are evidently the productions of a man who has not
seen nature with his own eyes; who has studied mineralogy in cabinets,
or in books only; but who has seldom beheld fossils in their native
place. With the balance in his hand, and the external characters of
WERNER in his view, he has examined minerals with diligence, and has
discovered many of those marks which serve to ascertain their places,
in a system of artificial arrangement. But to _reason_ and to _arrange_
are very different occupations of the mind; and a man may deserve
praise as a mineralogist, who is but ill qualified for the researches
of geology.
424. The same hurry and impatience are visible in the manner in which
his argument against Dr Hutton is usually conducted. He has seldom been
careful to make himself master of the opinions of his adversary; and
what he gives as such, and directs his reasonings against, have often
no resemblance to them whatsoever. Without any intention to deceive
others, but deceived himself, he usually begins with misrepresenting Dr
Hutton's notions, and then proceeds to the refutation of them. In this
imaginary contest, it will readily be supposed, that he is in general
successful: when a man has the framing both of his own argument, and
that of his antagonist, he must be a very unskilful logician if he does
not come off with the advantage.
425. It is but justice, however, to the Neptunists, to acknowledge,
that they are not all liable to the censure of beginning their
researches from a period antecedent to the existence of the laws of
nature. This absurdity does not, so far as I know, infect the system of
Werner. That mineralogist has not proposed to explain the first origin
of things, though he has supposed, at some former period, a condition
of the globe very unlike the present, viz. the entire submersion of the
solid under the fluid part.
NOTE XXIV. § 129.
_System of_ BUFFON.
426. The affinity of Dr Hutton's theory to that of Buffon, is nothing
more than what arises from their making use of the same agents, viz.
fire and water, in producing the present condition of the earth's
surface. In almost all other respects the two theories are extremely
different. The order in which those agents are employed in them, is
directly opposite, as has already been remarked; Buffon introducing the
action of fire first, and of water only in the second place, to waste
and destroy mineral bodies, and afterwards to dispose them anew, and
arrange them into strata. He makes no provision for the consolidation
of these strata, nor any for their angular elevation; he has no means
of explaining the unstratified rocks; nor any, but one extremely
imperfect, for explaining the inequalities of the earth's surface.
Again, Buffon mistook, in some degree, the true object of a theory of
the earth; and though he did not go back, like the geologists just
named, to a time when the laws of nature were not fully established,
he begins from a condition of things too unlike the present to be the
basis of any rational speculation. He does not, indeed, undertake to
examine the state of our planetary system before the sun existed; for
from such extravagance, even when most disposed to indulge his fancy,
he would surely have revolted. But he treats of the world, when the
earth and the planets had just ceased to be a part of the sun, and were
newly detached from the body of that luminary.[231]
[Footnote 231: According to Buffon, the granite is the true solar
matter, unchanged but by its congelation.]
This hypothesis concerning the origin of the planets, contrived chiefly
to account for the circumstance of their motion being all in the
same direction, and in other respects not only unsupported, but even
inconsistent with the principle of gravitation, has nothing in common
with a theory, confined as Dr Hutton's is, within the field which must
for ever bound our inquiries, and not venturing to speculate about the
earth, when in a condition totally different from the present.
427. In what relates to the future, the two systems are not more like
than in what relates to the past Buffon represents the cooling of our
planet, and its loss of heat, as a process continually advancing, and
which has no limit, but the final extinction of life and motion over
all the surface, and through all the interior, of the earth. The death
of nature herself is the distant but gloomy object that terminates
our view, and reminds us of the wild fictions of the Scandinavian
mythology, according to which, _annihilation_ is at last to extend
its empire even to the gods. This dismal and unphilosophic vision
was unworthy of the genius of Buffon, and wonderfully ill suited to
the elegance and extent of his understanding. It forms a complete
contrast to the theory of Dr Hutton, where nothing is to be seen beyond
the continuation of the present order; where no latent seed of evil
threatens final destruction to the whole; and where the movements are
so perfect, that they can never terminate of themselves. This is surely
a view of the world more suited to the dignity of NATURE, and the
wisdom of its AUTHOR, than has yet been offered by any other system of
cosmology.
428. I have often quoted Buffon in, the course of these
_Illustrations_, and most commonly for the purpose of combating his
opinions; but I am very sensible, nevertheless, of the obligations
under which he has laid all the sciences connected with the natural
history of the earth.
The extent and variety of his knowledge, the justness of his
reasonings, the greatness of his views, his correct taste, and manly
eloquence, qualified him, better, perhaps, than any other individual,
to compose the History of Nature. The errors into which he Has fallen,
are almost all the unavoidable consequences of the circumstances in
which he was placed; and if their amount is estimated by the proportion
that they bear to the general excellence of the work, they will be
reckoned but of small account. Buffon began to write when many parts
of natural history had made but little progress; when the quantity
of authentic information was small, and when scientific and correct
description was hardly to be found. Many of the greatest and most
important facts in geology were quite unknown, and scarcely any part
of the mineral kingdom had been accurately surveyed; and, with such
materials as this state of things afforded, it is not wonderful if
some parts of the edifice he erected have not proved so solid and
durable as the rest. Had he appeared somewhat later; had he been
farther removed from the time when reasonings _a priori_ usurped the
place of induction; and had he been as willing to correct the errors
into which he had been betrayed by imperfect information, as he was
ingenious in defending them, his work would probably have reached as
great perfection, as it is given for any thing without the sphere of
the accurate sciences to attain. If he had examined the natural history
of the earth more with his own eyes, and been as careful to delineate
it with fidelity as force; if he had listened with greater care to
the philosophers around him; had he attended to the demonstrations of
NEWTON more, and despised the arrangements of LINNÆUS less; he would
have produced a work, as singular for its truth as for its beauty, and
would have gone near to merit the eulogy pronounced by the enthusiasm
of his countrymen, MAJESTATI NATURÆ PAR INGENIUM.
NOTE XXV. § 130.
_Figure of the Earth._
429. That the earth is a spheroidal body, compressed at the poles,
or elevated at the equator, is a fact established by many accurate
experiments; and though these experiments do not exactly coincide, as
to the degree of oblateness which they give to that spheroid, they
agree sufficiently to put it beyond all dispute, that the earth, though
solid, has nearly the same figure which it would assume if fluid, in
consequence of its rotation on its axis.
Now, it is not at all obvious, to what physical cause this phenomenon
is to be ascribed. The earth, as it exists at present, has none of the
conditions that render the assumption of the figure of equilibrium in
any way necessary to it. Constituted as it is, its parts cohere with
forces incomparably too great to obey the laws of statical pressure,
or to assume any one figure rather than another, on account of the
centrifugal tendency which results from its revolution on its axis.
There is no necessity that its superficies should be every where level,
or perpendicular to the direction of gravity, nor that every two
columns, standing on the same base, any where within it, and reaching
from thence to any two points of the surface, should be of such weights
as precisely to balance one another. Neither of these, indeed, is at
all conformable to fact. They are, however, the very suppositions on
which the determination of the spheroid of equilibrium is founded; and
as they certainly do in no degree belong to the earth, it seems strange
that the result deduced from them should be in any way applicable to
it. This coincidence remains, therefore, to be explained; and it must
greatly enhance the merit of any geological system, if it can connect
this great and enigmatical phenomenon with the other facts in the
natural history of the earth.
430. To establish such a connection, has, accordingly, been a favourite
object with geologists, whether they have embraced the Neptunian or
Volcanic theory: both have thought that they were entitled to suppose
the primeval fluidity of the globe, the one by water, and the other
by fire; and in whatsoever way that fluidity was produced, the result
of it could be no other than the spheroidal figure of the whole mass,
agreeably to the laws of hydrostatics. If in this fluid state the earth
was homogeneous, the spheroid would be accurately elliptical, and the
compression at the poles would be 1/230 of the radius of the equator;
if the fluid was denser toward the centre, the flattening would be
less: and in either case, the body, as it acquired solidity, may be
supposed to have retained its spheroidal figure with little variation.
But though the fluidity of the earth will account for the phenomenon
of its oblate figure, it may reasonably be questioned, whether this
fluidity can be admitted, in consistency with other appearances.
According to what is established above, none of the appearances in the
mineral kingdom indicate more than a partial fluidity in any former
condition of the earth. The present strata, made up as they are of the
ruins of former strata, though softened by heat, have not been rendered
fluid by it, and have even possessed their softness in parts, and in
succession, not altogether, nor at the same time.
The unstratified, and more crystallized substances, were cast in the
bosom of others, which were solid at the time when they were fluid. In
all this, therefore, there is no indication of a fluidity prevailing
through the whole mass, or even over the whole surface of the earth,
and therefore nothing that can explain the spheroidal figure which it
has acquired. The supposition, then, of the entire body of the earth,
or even of its external crust, having been fluid, though it might
account for the compression at the poles, does not connect that fact
with the other facts in the natural history of the globe, and fails,
therefore, in the point most essential to a theory. It is liable, also,
to other objections, whether it be conceived to have proceeded from
fire or from water; whether it has happened on the principles of Buffon
or of Werner.
431. First, let us suppose that the fluidity of the earth, or of the
external crust of it, at least to a certain depth, proceeded from a
solution of the whole in the waters of the ocean; and, waving all the
objections that have been stated to this hypothesis, on account of
the absolute insolubility of many mineral substances in water, let us
suppose them all soluble in a certain degree, and let us compute the
quantity of the menstruum, which, on the suppositions most favourable
to the system, must have been required to this great geologico-chemical
operation.
The siliceous earth, though not soluble in water _per se_, yet, after
being dissolved in that fluid by means of an alkali, was found by Dr
Black, in his analysis of the Geyser water, to remain suspended in a
quantity of water, between 500 and 1000 times its own weight. This is
one of the facts most favourable to the Neptunian theory; and that
every advantage may be given to that theory, we shall take the least of
the numbers just mentioned, and suppose that siliceous earth may be
dissolved or suspended in 500 times its weight of water.
Taking this for the extreme degree of insolubility of mineral
substances, (though there are many of which the insolubility is
absolute, or, to speak in the language of calculation, infinitely
great,) we may suppose the insolubility of all the rest, or the
quantities of water in which they are dissolved, to be ranged in a
descending scale from 500 to 0, the extreme degree of deliquescence.
Then, taking the arithmetical mean between these extremes, it will give
us 250, as the proportion of water in which mineral substances may at
an average be dissolved. But this average is much less than the truth;
for the quantity of siliceous earth is great in comparison of any of
the rest, and the mineral substances that are extremely soluble in
water are but in a small quantity; therefore, when we suppose mineral
bodies, at a medium, to be soluble in 250 times their own weight of
water, we make a supposition extremely favourable to the Neptunian
system.
432. This is the proportion between the _weight_ of the solvent, and
of the substances held in solution: to have the proportion of their
_bulks_, we may suppose the specific gravity of mineral bodies in
general to be to that of water as 5 to 2, and then we have the ratio
of bulks, that of 250 × 5 to 2 × 1, or of 625 to 1. It follows, then,
that minerals in general cannot be supposed soluble in less than 625
times their bulk of water.
433. Again, it must be allowed to the Neptunists, that the fluidity
of the whole earth is not necessary to account for its assuming the
spheroidal figure. It is sufficient if the whole of that crust or shell
of matter was fluid, which is contained between the actual surface
of the terrestrial spheroid, and the surface of the sphere inscribed
within it; that is, of the sphere which has for its diameter the polar
axis of the earth. The whole of the minerals which compose this shell,
must at least have been dissolved in water, and have formed the chaotic
mass of Mr Kirwan. The volume of the water required for this was not
less than 625 times the bulk of the spheroidal shell that has just been
mentioned.
But, assuming the difference between the polar axis and the equatorial
diameter to be 1/300 of the latter, which is the supposition most
agreeable to the phenomena, it is easy to show that the magnitude of
the above spheroidal shell, or the difference between the solid content
of the earth, and the sphere inscribed in it, is greater than 1/151 and
less than 1/150 of the whole earth; so that the earth is less than 151
times the spheroidal shell.
The volume of the water, therefore, necessary to hold in solution the
materials of this shell, is to the volume of the whole earth as 625
to 151, or in a greater ratio than that of four to one: and such,
therefore, at the very least, is the quantity of water which Mr Kirwan
supposes, after it ceased to act in its chemical capacity, to have
retired into caverns in the interior of the earth. Thus the Neptunists,
in their account of the spheroidal figure of the earth, are reduced
to a cruel dilemma, and are forced to choose between a physical and a
mathematical impossibility.
If we would inquire whether the opinion of the igneous origin of
minerals, as commonly received by the Vulcanists, is capable of
affording a better solution of this difficulty, the theory of M. de
Buffon is the first that presents itself.
434. That philosopher considers the existence of the spheroidal figure
as a proof that the whole of the earth must have been originally fluid;
and as the fluidity of the whole can only be ascribed to fusion, he has
supposed that the earth was originally a mass of melted matter struck
off from the sun by the collision of a comet; and that this mass, when
made to revolve on its axis, put on a spheroidal figure, which it has
retained, though now cooled down to congelation.
This system need not be considered in detail; the foundation of it is
laid in such defiance of the principles of geometry and mechanics, that
the architect, notwithstanding all the fertility of his invention, and
all the resources of his genius, was never able to give any solidity to
the structure.
But it will be said, that we may take a part of the system, without
venturing on the whole, and may suppose that the earth, or at least
the external crust of it, has been fluid by fire, though we do not
inquire into the cause of this fire, or into the manner in which it was
produced.
It is indeed true, that, when this is done, we have not the same sort
of absurdity to encounter that we met with in the Neptunian system, and
that the Volcanic theory does not, like it, come into direct collision
with an axiom of geometry. There are, nevertheless, great objections
to it; for though all the phenomena of the mineral kingdom attest a
fluidity of igneous origin, yet it is a fluidity that was never more
than partial; and though it has been over all the earth, has been over
it in succession only. Besides, we are not entitled to assume the
existence, and again the disappearance of such a great quantity of
heat, without assigning some cause for the change.
435. Since, then, neither the hypothesis of the Neptunists or the
Vulcanists, affords any good explanation of the figure of the earth, or
such a one as can connect it with the other appearances in its natural
history, it remains to inquire, whether the system that supposes a
partial and successive fluidity, like Dr Hutton's, has any resource for
explaining this great phenomenon.
Of this subject Dr Hutton has not treated; and when I was first made
acquainted with his system, it appeared to me a very serious objection
to it, that it did not profess to give an explanation of so important
a fact as the oblate figure of the earth. On considering the matter
more closely, however, I found that there were principles contained
in it from which a very satisfactory solution (and, I think, the only
satisfactory solution) of that difficulty might be deduced. This
solution I shall endeavour to explain, in as far, at least, as is
necessary for the purpose of general illustration.
It is laid down in Dr Hutton's theory, that the surface of the earth is
perpetually changed by the _detritus_ of the land; and that from the
materials thus afforded, new horizontal strata are perpetually formed
at the bottom of the sea. If this be true, and if the alternations of
decay and renovation have been often repeated, it is certain, that the
figure of the earth, whatever it may have originally been, must be
brought at length to coincide with the spheroid of equilibrium.
436. Here it is necessary to remark, that the expressions, _figure of
the earth_, and _surface of the earth_ are each of them occasionally
taken in two different senses.
The surface of the earth, in its most obvious sense, is that which
bounds the whole earth, and includes all its inequalities; it is a
surface extremely irregular, rising to the tops of the mountains,
descending to the bottoms of the valleys, and having the continuity
of its curvature often interrupted, or suddenly changed. This may be
called the _actual_ surface, and the figure bounded by it, the _actual_
figure, of the earth.
The surface of the earth, in another sense, is one that is every where
horizontal, and is the same which water assumes when at rest.
This superficies is determined by the circumstance of its being
constantly perpendicular to the direction of gravity; it is the surface
marked out by levelling, and may be supposed to be continued from the
sea, through the interior of the land, till it meet the sea again. The
figure bounded by this horizontal surface, may properly be called the
_statical_ figure of the earth.
When it is said that the figure of the earth is an oblate spheroid, it
is the statical, not the actual figure which is meant; and the degrees
of the meridian which astronomers measure, are also referred to the
superficies of the former.
437. Suppose now a body like the earth, but with its actual figure
infinitely more irregular, having a sea circumfused around it, the
water will descend into the lowest situations, and will so arrange
itself, that its surface shall be perpendicular every where to the
plumb-line, or to the direction of gravity, in which state only it can
remain at rest. The figure of the superficies which the sea must thus
take will be of a continuous curvature, and will return into itself;
though it may, if the actual figure is very irregular, be far either
from a sphere or a spheroid. If, however, we suppose the solid parts
of this mass subject to be dissolved or worn away, and carried down to
the ocean, there will be a tendency to give to the whole body the same
figure that it would have assumed, if it had been entirely fluid, and
subject to the laws of hydrostatics. This tendency is the result of
two principles.
438. Let us suppose the body just described to have no rotation, so
that the particles of it are actuated only by the forces of cohesion
and of attraction.
It is then clear, that every particle taken away by attrition from the
parts above the level of the sea, and deposited under the surface of
it, makes the general figure more compact, bringing the remoter parts
nearer to the centre of gravity of the whole; so that, in time, if the
body is homogeneous, all the points of the surface will become equally
distant from that centre. Thus the _actual_ figure changes continually,
and approaches nearer to the _statical_.
While this change is going forward in the actual figure, there is
another produced on the statical, that tends very much to accelerate
the final coincidence, of the two.
The effect of the inequalities of the land, that rise above the
horizontal surface, is, by their attraction, to render the parts of
that surface immediately under them, more convex, _cæteris paribus_,
than the rest. Again, where there are parts of extraordinary depth in
the sea, that is, where the solid and denser parts are far removed from
the surface of the ocean, the curvature of the superficies of the sea
is thereby diminished, and that superficies is rendered less convex
than it would be if the sea were shallower. These propositions are both
capable of strict mathematical demonstration. Hence the taking away of
any particle of matter from the top of a mountain tends to diminish the
curvature of the horizontal surface under the mountain, where it is
greatest; and the deposition of the same particle at the bottom of the
sea, tends to increase the curvature of this superficies where it is
least. The general tendency, therefore, being to increase the curvature
where it is least, and to diminish it where it is greatest, must be
to bring about an uniform curvature throughout, that is, a spherical
figure. Thus, by the waste and subsequent stratification of the land,
the direction of gravity is continually altered; it is more and more
concentrated, and the figure brought nearer to that which a fluid would
assume.
439. If now we suppose the body to revolve on its axis, all other
things remaining as before, the surface bounding the sea will become
different from what it was in the former case, and will be more swelled
out toward the middle or equatorial regions. The land above the level
of the sea will still, as before, be worn down and deposited in the
bottom of the sea, so as to form strata nearly parallel to its surface:
the tendency, therefore, is to render the real figure of the planet
nearer to the statical. At the same time the _statical_ figure is
changed, as explained above; so that the two figures mutually approach,
and the limit, or ultimate figure to which they tend, is one over which
the ocean might be diffused every where to the same depth, for then the
causes of change would entirely cease. But this figure is no other than
the spheroid of equilibrium, which, therefore, is the effect which the
waste and reconsolidation of the land would necessarily produce, if the
process were continued indefinitely, without interruption. In this, as
in many other instances, when a body is subject to the action of causes
by which its form is _gradually_ changed, the figure best adapted
to resist those changes, is the figure which the changes themselves
ultimately produce.
Also, whatever be the irregularities of density, the tendency to a
change of figure will not cease till the body is moulded into that
particular spheroid which admits of being covered with water every
where to the same depth.[232] Thus it appears, that a solid of an
irregular figure, and of irregular density, provided it be in part
covered with water; and be at the same time subject to waste above the
surface of the sea, and reconsolidation under it, has a tendency to
acquire, in time, the same figure that it would have acquired had it
been entirely fluid.
[Footnote 232: In the same manner as a transition is thus made from an
irregular figure to a spheroid of equilibrium, so, if the actual figure
were at first more simple than the spheroid, it would still be changed
into this last by degrees.
Let us conceive, for instance, that the earth is at rest, and is a
perfect sphere of solid matter, surrounded by an ocean every where of
equal depth, for example, of one mile. Then, if a rotatory motion be
communicated to it, so that it shall revolve on its axis in twenty-four
hours, in consequence of the centrifugal force, the water circumfused
about the sphere will immediately rise up under the equator, and will
become part of a spheroidal surface, (not elliptical, but nearly so,)
the equatorial diameter of which is greater than the polar axis, in the
ratio of 588 to 577 By this means the water will be accumulated at the
equator to the depth of nearly 2.5 miles, and form a zone surrounding
the earth, and extending about 37° on each side of the equator. The
remainder of the surface will be left dry, forming two vast circumpolar
continents, that reach 53° on every side of the poles, and that are
elevated in the middle more than four miles above the level of the sea.
Such would be the state of our globe, on the hypothesis above laid
down; and, if there were no waste or destruction of the land, this
order of things would be permanent, and neither the solid nor fluid
part of the mass could ever acquire any other figure than that which
has been described. But, if the same laws be supposed to regulate the
action of the atmosphere in those circumstances, that do actually
regulate it according to the present constitution of the globe, the
vapours raised up from the surface of the sea, would be carried by the
winds over the land, where they would be condensed and precipitated in
rain. Thus, all the agents of destruction would be let loose on the two
great circumpolar continents; rivers would be formed; the land would
become deeply intersected by ravines; those ravines would gradually
open into wide valleys; the masses of greatest resistance would be
shaped into hills and mountains: and from a superficies originally
smooth and uniform, the same inequalities would be produced which at
present diversify the surface of the earth.
While the parts of the sphere without the spheroid are thus continually
diminished, the loose earth and sand washed down from them, will be
deposited at the bottom of the sea, and will form strata parallel
to the surface of the superincumbent water. The actual and statical
figure are thus brought nearer one another; and, at the same time the
statical is changed, on the principle already explained, (the change in
the direction of gravity,) and is made continually to approximate to a
state, which when it has attained, no farther change can take place,
viz. an oblate elliptic spheroid, of which the surface is perpendicular
to the direction of gravity, having the equatorial diameter to the
polar axis in the ratio of 230 to 229.]
440. In the preceding reasonings, we have supposed the process of decay
and subsequent stratification to be carried on without interruption,
till the whole of the land is covered by the sea. This supposition is
useful for explaining the nature of the forces which have determined
the figure of the earth; but there is no reason to think that it has
ever been realized in its full extent, the elevation of strata from the
bottom of the sea interrupting the progress, and producing new land
in one place, as the old decays in another. The very same land also,
which is wasted at its surface, may perhaps be lifted up by the forces
that are placed under it; or it may be let down, undergoing alterations
of its level, from causes that we do not perceive, but of which the
action is undoubted, (§ 388.) But notwithstanding these interruptions,
the general tendency to produce in the earth a spheroidal figure may
remain, and more may be done by every revolution, to bring about the
attainment of that figure than to cause a deviation from it. This
figure, therefore, though never likely to be perfectly acquired, will
be the _limiting_ or _asymptotic_ figure, if it may be so called, to
which the earth will continually approach.
441. If the preceding conclusions are just, and if the figure of
equilibrium is only an asymptotic figure, to which that of the earth
may approximate, but cannot perfectly attain, we are not to be
surprised if considerable deviations from it are actually observed.
This has accordingly happened, insomuch, that the results deduced from
the most accurate measurement of degrees of the meridian, differ from
one another, in the oblateness they give to the earth, by nearly one
half of the quantity to be determined. When we compare the degrees
measured in France, and in some other countries of Europe, with
those measured in Peru, we obtain for the compression at the poles,
less than 1/300 of the radius of the earth. But when we compare the
degrees measured in France with one another, and with those lately
measured in England, we find that they are best represented by a
spheroid that has its compression 1/150 of its semi-axis.[233] There
is reason to think, therefore, that the meridians are not elliptical;
and other observations seem to show, that they are not even similar
to one another; or that the earth is not, strictly speaking, a solid
of revolution; so, also, the comparison of the degree measured at
the Cape of Good Hope, with those measured on the opposite side of
the equator, creates a suspicion, that the northern and southern
hemispheres are not perfectly alike, and that the earth is not equally
compressed at the Arctic and the Antarctic poles. These irregularities,
though they do not affect the general fact of the earth's compression
at the poles, show that the true statical figure is but imperfectly
attained; and though this may be accounted for, without having recourse
to the principles involved in our theory, it is in a manner very
unsatisfactory, and, by help of suppositions, not at all consistent
with the original fluidity ascribed to the whole mass, or to the
exterior crust of the earth.
[Footnote 233: Exposition du Systéme du Monde, par La Place, p. 61, 2d
edit.]
442. As the principles here laid down explain how a solid body may
attain very nearly the figure which a fluid would acquire in order to
preserve its parts in equilibrium; and since the oblate figure belongs
to other of the planets as well as the earth, and the globular to all
the great bodies of the universe, this suggests an analogy that goes
deep into the economy of nature, and extends far beyond the limits
within which the mineralogist is wont to confine his speculations.
443. That no very irregular figure is found among the planetary bodies,
may therefore be considered as a proof of the universality of that
system of waste and reconsolidation that we have been endeavouring to
trace in the natural history of the earth. A farther proof of the same
arises from considering, that for every given mass of matter, having a
given period of rotation, there are two different spheroids that answer
the conditions of establishing an equilibrium among its parts, the one
near to the sphere, and the other very distant from it, and so oblate
as to have a lenticular form. Thus the earth, supposing it homogeneous,
might either be in equilibrium, by means of the figure which it
actually has, or of one in which the polar was to the equatorial
diameter as 1 to 768. The same is true of the other planets; and yet we
no where find that this highly compressed spheroid is actually employed
by nature. The reason, no doubt, is, that in so oblate a spheroid, the
equilibrium between the gravitating and the centrifugal force is of
the kind that does not re-establish itself when disturbed; so that the
parts let loose, and not kept in their place by firm cohesion, would
fly off altogether. In such a body, the waste at the surface would
lead to an entire change of form, and therefore the constitution here
supposed could not be permanent.
444. In the system of Saturn, we have a great deviation from the
general order, which, nevertheless, has led to a very unexpected
verification of some of the conclusions deduced above. A principle
extremely like that which is the basis of all the foregoing reasonings,
led one of the greatest philosophers of the present age to discover
the revolution of Saturn's ring on its axis, and even to determine
the velocity of that revolution, such as it has been since found by
observation. LA PLACE, laying it down as a maxim, that nothing in
nature can exist, where there are causes of change, not balanced or
compensated by other causes,[234] concluded, that the-parts of the
ring must be held from falling down to the body of the planet by some
other force than their mere cohesion to one another. Were it otherwise,
every particle detached from the ring, by any means, must descend in a
straight line, almost perpendicular to the surface of Saturn; and the
final destruction of the ring must be inevitable. The only force that
could balance this effect of gravitation, seemed to be a centrifugal
force, arising from the rotation of the ring on an axis passing through
its centre, and perpendicular to its plane. La Place proceeded to
inquire what celerity of rotation was adequate to this effect, and
found that one of ten hours and a quarter would be required, which
is almost precisely the time afterwards determined by Dr HERSCHEL
from actual observation. If, with this rotation, the ring is a solid
annulus generated by the rotation of a very flat ellipsis about a given
point in its greater axis, coinciding with the centre of Saturn, it may
be so constituted, that the attraction of Saturn, combined with the
centrifugal force, may produce a force perpendicular to its surface,
and may enable detached parts to remain at rest, animals, for instance,
to walk on its surface, and fluids to be _in equilibrio_. The system of
Saturn is thus fortified against the lapse of time, as effectually as
that of the earth itself; and the means by which this is accomplished,
seem to prove, that the weapons which time employs, are in both cases
the same, viz. the slow wearing and decomposition of the solid parts.
This slow wearing may have produced the figure by which its action is
most effectually resisted.
[Footnote 234: La Place, _ubi supra_, p. 242.]
445. Thus Dr Hutton's theory of the earth comes at last to connect
itself with the researches of physical astronomy. The conclusion to be
drawn from this coincidence is to the credit of both sciences. When two
travellers, who set out from points so distant as the mineralogist and
the astronomer, and who follow routes so different, meet at the end of
their journey, and agree in their report of the countries through which
they have passed, it affords no slight presumption, that they have kept
the right way, and that they relate what they have actually seen.
NOTE XXVI. § 133.
_Prejudices relating to
the Theory of the Earth._
446. Among the prejudices which a new theory of the earth has to
overcome, is an opinion, held, or affected to be held, by many, that
geological science is not yet ripe for such elevated and difficult
speculations. They would, therefore, get rid of these speculations, _by
moving the previous question_, and declaring that at present we ought
to have no theory at all. We are not yet, they allege, sufficiently
acquainted with the phenomena of geology; the subject is so various and
extensive that our knowledge of it must for a long time, perhaps for
ever, remain extremely imperfect. And hence it is, that the theories
hitherto proposed have succeeded one another with so great rapidity,
hardly any of them having been able to last longer than the discovery
of a new fact, or a fact unknown when it was invented. It has proved
insufficient to connect this fact with the phenomena already known, and
has therefore been justly abandoned. In this manner, they say, have
passed away the theories of Woodward, Burnet, Whiston, and even of
Buffon; and so will pass, in their turn, those of Hutton and Werner.
447. This unfavourable view of geology, ought not, however, to be
received without examination; in science, presumption is less hurtful
than despair, and inactivity is more dangerous than error.
One reason of the rapid succession of geological theories, is the
mistake that has been made as to their object, and the folly of
attempting to explain by them the first origin of things. This mistake
has led to fanciful speculations that had nothing but their novelty to
recommend them, and which, when that charm had ceased, were rejected
as mere suppositions, incapable of proof. But if it is once settled,
that a theory of the earth ought to have no other aim but to discover
the laws that regulate the changes on the surface, or in the interior
of the globe, the subject is brought within the sphere either of
observation or analogy; and there is no reason to suppose, that man,
who has numbered the stars, and measured their forces, shall ultimately
prove unequal to this investigation.
448. Again, theories that have a rational object, though they be false
or imperfect in their principles, are for the most part approximations
to the truth, suited to the information at the time when they were
proposed. They are steps, therefore, in the advancement of knowledge,
and are terms of a series that must end when the real laws of nature
are discovered. It is, on this account, rash to conclude, that in the
revolutions of science, what has happened must continue to happen,
and because systems have changed rapidly in time past, that they must
necessarily do so in time to come.
He who would have reasoned so, and who had seen the ancient physical
systems, at first all rivals to one another, and then swallowed up by
the Aristotelian; the Aristotelian physics giving way to those of Des
Cartes; and the physics of Des Cartes to those of Newton; would have
predicted that these last were also, in their turn, to give place to
the philosophy of some later period. This is, however, a conclusion
that hardly any one will now be bold enough to maintain, after a
hundred years of the most scrupulous examination have done nothing
but add to the evidence of the NEWTONIAN SYSTEM. It seems certain,
therefore, that the rise and fall of theories in times past, does not
argue, that the same will happen in the time that is to come.
449. The multifarious and extremely diversified object of geological
researches, does, no doubt, render the first steps difficult, and
may very well account for the instability hitherto observed in such
theories; but the very same thing gives reason for expecting a very
high degree of certainty to be ultimately attained in these inquiries.
Where the phenomena are few and simple, there may be several different
theories that will explain them in a manner equally satisfactory;
and in such cases, the true and the false hypotheses are not easily
distinguished from one another. When, on the other hand, the phenomena
are greatly varied, the probability is, that among them, some of
those _instantiæ crucis_ will be found, that exclude every hypothesis
but one, and reduce the explanation given to the highest degree of
certainty. It was thus, when the phenomena of the heavens were but
imperfectly known, and were confined to a few general and simple facts,
that the Philolaic could claim no preference to the Ptolemaic system:
The former seemed a possible hypothesis; but as it performed nothing
that the other did not perform, and was inconsistent with some of our
most natural prejudices, it had but few adherents. The invention of the
telescope, and the use of more accurate instruments, by multiplying
and diversifying the facts, established its credit; and when not only
the general laws, but also the inequalities, and disturbances of the
planetary motions were understood, all physical hypotheses vanished,
like phantoms, before the philosophy of NEWTON. Hence the number, the
variety, and even the complication of facts, contribute ultimately to
separate truth from falsehood; and the same causes which, in any case,
render the first attempts toward a theory difficult, make the final
success of such attempts just so much the more probable.
This maxim, however, though a general encouragement to the prosecution
of geological inquiries, does not amount to a proof that we are yet
arrived at the period when those inquiries may safely assume the form
of a theory. But that we are arrived at such a period, appears clear
from other circumstances.
450. It cannot be denied, that a great multitude of facts, respecting
the mineral kingdom, are now known with considerable precision; and
that the many diligent and skilful observers, who have arisen in the
course of the last thirty years, have produced a great change in the
state of geological knowledge. It is unnecessary to enumerate them
all; FERBER, BERGMAN, DE LUC, SAUSSURE, DOLOMIEU, are those on whom
Dr Hutton chiefly relied; and it is on their observations and his own
that his system is founded. If it be said, that only a small part of
the earth's surface has yet been surveyed, and described with such
accuracy as is found in the writers just named, it may be answered,
that the earth is constructed with such a degree of uniformity, that a
tract of no very large extent may afford instances of all the leading
facts that we can ever observe in the mineral kingdom. The variety of
geological appearances which a traveller meets with, is not at all in
proportion to the extent of country he traverses; and if he take in a
portion of land sufficient to include primitive and secondary strata,
together with mountains, rivers, and plains, and unstratified bodies in
veins and in masses, though it be not a very large part of the earth's
surface, he may find examples of all the most important facts in the
history of fossils. Though the labours of mineralogists have embraced
but a small part of the globe, they may therefore have comprehended a
very large proportion of the phenomena which it exhibits; and hence a
presumption arises, that the outlines, at least, of geology have now
been traced with tolerable truth, and are not susceptible of great
variation.
451. When the phenomena of any class are in general ambiguous, and
admit of being explained by different or even opposite theories; if few
of those exclusive facts are known, which admit but of one or a few
solutions, then we have no right to expect much from our endeavours to
generalise, except the knowledge of the points where our information
is most deficient, and to which our observations ought chiefly to be
directed. But that many of the exclusive and unambiguous instances are
known, in the natural history of the globe, I think is evident from the
reasoning in the foregoing pages, where so many examples have occurred
of appearances that give the most direct negative to the Neptunian
system, and exclude it from the number of possible hypotheses, by
which the phenomena of geology can be explained. The abundance of such
instances is an infallible sign, that the mass of knowledge is in that
state of fermentation, from which the true theory may be expected to
emerge.
452. Another indication of the same kind, is the near approach that
even the most opposite theories make, in some respects, to one another.
There are so many points of contact between them, that they appear
to approximate to an ultimate state, in which, however unwillingly,
they must at last coincide. That ultimate form, too, which all these
theories have a tendency to put on, if I am not deceived, is no other
than that of the Huttonian theory.
453. The first example I shall take from the system of Saussure. It
is to be regretted, that this excellent geologist has no where given
us a complete account of his theory. Some of the leading principles
of it are, however, unfolded in the course of his observations, and
enable us to form a notion of its general outline. It was evidently far
removed from the system of subterraneous heat, and seems, especially
in the latter part of the author's life, to have been very much
accommodated to the prevailing system of WERNER. Nevertheless, with
so little affinity between their general views, Saussure and Hutton
agree in that most important article which regards the elevation of
the strata. Saussure plainly perceived the impossibility of the strata
being formed in the vertical situations which so many of them now
occupy; and he takes great pains to demonstrate this impossibility,
from some facts that have been referred to above. He also believed that
this elevation had been given to strata that were originally level, by
a force directed upwards, or by the _refoulement_ of the beds, not by
their falling in, as is the opinion of De Luc and some other of the
Neptunists.
Now, whoever admits this principle, and reasons on it consistently,
without being afraid to follow it through all its consequences, must
unavoidably come very close to the Huttonian theory. He must see,
that a power which, acting from below, produced this great effect
can never have belonged to water, unless rarefied into steam by the
application of heat. But if it be once admitted that heat resides in
the mineral regions, the great objection to Dr Hutton's system is
removed; and the theorist, who was furnished with so active and so
powerful an agent, would be very unskilful in the management of his
own resources, if he did not employ it in the work of consolidating as
well as in that of raising up the strata. A little attention will show,
that it is qualified for both purposes; though insuperable objections
must, no doubt, offer themselves, where the effects of compression
are not understood. We may safely conclude, then, that the accurate
and ingenious Geologist of Geneva ought to have been a _Plutonist_,
in order to give consistency to the principles which he had adopted,
and to make them coalesce as parts of one and the same system. If he
embraced an opposite opinion, it probably was from feeling the force of
those objections that arise from our discovering nothing in the bowels
of the earth like the remains left by combustion, or inflammation, at
its surface. The secret by which these seeming contradictions are to be
reconciled, was unknown to this mineralogist, and he has accordingly
decided strongly against the action of fire, even in the case of those
unstratified substances that have the greatest affinity to volcanic
lava.
454. The theoretical conclusions of another accurate and skilful
observer, Dolomieu, furnish a still more remarkable example of a
tendency to union between systems professedly hostile to one another.
This ingenious mineralogist, observing the interposition of the basalt
between stratified rocks, so that it had not only regular beds of
sandstone for its base, but was also covered with beds of the same
kind, saw plainly that these appearances were inconsistent with the
supposition of common volcanic explosions at the surface. He therefore
conceived, that the volcanic eruption had happened at the bottom of
the sea, (the level of which, in former ages, had been much higher
than at present,) and that the materials afterwards deposited on the
lava, had been in length of time consolidated into beds of stone. It
is evident, that this notion of submarine volcanoes, comes very near,
in many respects, to Dr Hutton's explanation of the same appearances.
If the only thing to be accounted for were the phenomenon in question,
it cannot be denied that Dolomieu's hypothesis would be perfectly
sufficient; but Dr Hutton, to whom this phenomenon was familiar, and
who, like Dolomieu, conceived the basalt to have been in fusion, was
convinced that the retreat of the sea was not a fact well attested by
geological appearances, and if admitted, was inadequate to account for
the facts usually explained by it. He conceived, therefore, that such
lava as the preceding had flowed not only at the bottom of the sea,
but in the bowels of the earth, and having been forced up through the
fissures of rocks already formed, had heaved up some of these rocks,
and interposed itself between them. This agrees with the other facts in
the natural history both of the basaltes and the strata.
It is plain, that, in this, there is a great approach of the two
theories to one another: both maintain the igneous origin of basaltes,
and its affinity to lava; both acknowledge that this lava cannot have
flowed at the surface, and that the strata which cover it have been
formed at the bottom of the sea. They only differ as to the mode in
which the submarine or subterraneous volcano produced its effect, and
that difference arises merely from the one geologist having generalized
more than the other. Dolomieu sought to connect the basalt with the
lavas that proceed from volcanic explosions at the surface; Dr Hutton
sought not only to connect these two appearances with one another, but
also with the other phenomena of mineralogy, particularly with the
veins of basaltes, and the elevation of the strata.
455. In another point, the coincidence of Dolomieu's opinions and Dr
Hutton's is still more striking. The former has remarked, that many
of the extinguished volcanoes are in granite countries, and that,
nevertheless, the lavas that they have erupted contain no granitic
stones. There must be, therefore, says he, something under the granite,
and this last is not, at least in all cases, to be considered as the
basis of the mineral kingdom, or as the body on which all others rest.
In this system, therefore, granite is not always a primordial rock, any
more than in Dr Hutton's.
But Dolomieu makes a still nearer advance to the Huttonian theory; for
he supposes, that under the solid and hard crust of the globe, there is
a sphere of melted stone, from which this basaltic lava was thrown up.
The system of subterraneous heat is here adopted in its utmost extent,
and in that form which is considered as the most liable to objection,
viz. the existence of it at the present moment, in such a degree as to
melt rocks, and keep them in a state of fusion. In this conclusion, the
two theories agree perfectly; and if they do so, it is only because
the nature of things has forced them into union, notwithstanding the
dissimilitude of their fundamental principles.
This ought to be considered as a strong proof, that the phenomena
known to mineralogists are sufficient to justify the attempts to form
a theory of the earth, and are such as lead to the same conclusions,
where there was not only no previous concert, but even a very marked
opposition. I have already observed, that there is a greater tendency
to agree among geological theories, than among the authors of those
theories.
456. Another circumstance worthy of consideration is, that in the
search which the Neptunists have made, for facts most favourable to the
aqueous formation of minerals, we find hardly any of a kind that was
unknown to the author of the system here explained. The appearances on
which WERNER grounds his opinion with respect to basaltes, and by which
he would exclude the action of fire from any share in the formation of
it, are all comprehended in the alternation of that rock with beds, or
strata obviously of aqueous origin. Now these appearances were well
known to Dr Hutton, and are easily explained by his theory, provided
the effects of compression are admitted. From this, and the other
circumstances just observed, I am disposed to think, that the great
facts on which every geological system must depend, are now known, and
that it is not too bold an anticipation to say, that a theory of the
earth, which explains all the phenomena with which we are at present
acquainted, will be found to explain all those that remain to be
discovered.
457. The time indeed was, and we are not yet far removed from it,
when one of the most important principles involved in Dr Hutton's
theory was not only unknown, but could not be discovered. This was
before the causticity produced in limestone by exposure to fire was
understood, and when it was not known that it arose from the expulsion
of a certain aerial fluid, which before was a component part of the
stone. It could not then be perceived, that this aerial part might be
retained by pressure, even in spite of the action of fire, and that in
a region where great compression existed, the absence of causticity was
no proof that great heat had not been applied. The discoveries of Dr
BLACK, therefore, mark an era, before which men were not qualified to
judge of the nature of the powers that had acted in the consolidation
of mineral substances. Those discoveries were, indeed, destined to
produce a memorable change in chemistry, and in all the branches of
knowledge allied to it; and have been the foundation of that brilliant
progress, by which a collection of practical rules, and of insulated
facts, has in a few years risen to the rank of a very perfect science.
But even before they had explained the nature of carbonic gas, and its
affinity to calcareous earth, I am not sure but that Dr Hutton's theory
was, at least, partly formed, though it must certainly have remained,
even in his own opinion, exposed to great difficulties. His active and
penetrating genius soon perceived, in the experiments of his friend,
the solution of those difficulties, and formed that happy combination
of principles, which has enabled him to explain the most enigmatical
appearances in the natural history of the earth.
As we are not yet far removed from the time when our chemical knowledge
was too imperfect to admit of a satisfactory explanation of the
phenomena of mineralogy, so it is not unlikely that we are approaching
to other discoveries that are to throw new light on this science. It
would, however, be to argue strangely to say, that we must wait till
those discoveries are made before we begin any theoretical reasonings.
If this rule were followed, we should not know where the imperfections
of our science lay, nor when the remedies were found out, should we
be in a condition to avail ourselves of them. Such conduct would not
be caution, but timidity, and an excess of prudence fatal to all
philosophical inquiry.
458. The truth, indeed, is, that in physical inquiries, the work of
theory and observation must go hand in hand, and ought to be carried
on at the same time, more especially if the matter is very complicated,
for there the clue of theory is necessary to direct the observer.
Though a man may begin to observe without any hypothesis, he cannot
continue long without seeing some general conclusion arise; and to this
nascent theory it is his business to attend, because, by seeking either
to verify or to disprove it, he is led to new experiments, or new
observations. He is led also to the very experiments and observations
that are of the greatest importance, namely, to those _instantiæ
crucis_, which are the _criteria_ that naturally present themselves
for the trial of every hypothesis. He is conducted to the places where
the transitions of nature are most perceptible, and where the absence
of former, or the presence of new circumstances, excludes the action
of imaginary causes. By this correction of his first opinion, a new
approximation is made to the truth; and by the repetition of the same
process, certainty is finally obtained. Thus theory and observation
mutually assist one another; and the spirit of system, against which
there are so many and such just complaints, appears, nevertheless, as
the animating principle of inductive investigation. The business of
sound philosophy is not to extinguish this spirit, but to restrain and
direct its efforts.
459. It is therefore hurtful to the progress of physical science to
represent observation and theory as standing opposed to one another.
Bergman has said, "Observationes veras quàm ingeniosissimas fictiones
sequi præstat; naturæ mysteria potius indagare quàm divinare."
If it is meant by this merely to say, that it is better to have facts
without theory, than theory without facts, and that it is wiser to
inquire into the secrets of nature, than to guess at them, the truth
of the maxim will hardly be controverted. But if we are to understand
by it, as some may perhaps have done, that all theory is mere fiction,
and that the only alternative a philosopher has, is to devote himself
to the study of facts unconnected by theory, or of theory unsupported
by facts, the maxim is as far from the truth, as I am convinced it is
from the real sense of Bergman. Such an opposition between the business
of the theorist and the observer, can only occur when the speculations
of the former are vague and indistinct, and cannot be so embodied as to
become visible to the latter. But the philosopher who has ascended to
his theory by a regular generalization of facts, and who descends from
it again by drawing such palpable conclusions as may be compared with
experience, furnishes the infallible means of distinguishing between
_perfect science_ and _ingenious fiction_. Of a geological theory that
has stood this double test of the analytic and synthetic methods, Dr
Hutton has furnished us with an excellent instance, in his explanation
of granite. The appearances which he observed in that stone led him to
conclude, that it had been melted, and injected while fluid, among the
stratified rocks already formed. He then considered, that if this is
true, veins of granite must often run from the larger masses of that
stone, and penetrate the strata in various directions; and this must
be visible at those places where these different kinds of rock come
into contact with one another. This led him to search in Arran and
Glentilt for the phenomena in question; the result, as we have seen,
afforded to his theory the fullest confirmation, and to himself the
high satisfaction which must ever accompany the success of candid and
judicious inquiry.
460. It cannot, however, be denied, that the impartiality of an
observer may often be affected by system; but this is a misfortune
against which the want of theory is not always a complete security.
The partialities in favour of opinions are not more dangerous than
the prejudices against them; for such is the spirit of system, and so
naturally do all men's notions tend to reduce themselves into some
regular form, that the very belief that there can be no theory, becomes
a theory itself, and may have no inconsiderable sway over the mind
of an observer. Besides, one man may have as much delight in pulling
down, as another has in building up, and may choose to display his
dexterity in the one occupation as well as in the other. The want
of theory, then, does not secure the candour of an observer, and it
may very much diminish his skill. The discipline that seems best
calculated to promote both, is a thorough knowledge of the methods of
inductive investigation; an acquaintance with the history of physical
discovery; and the careful study of those sciences in which the rules
of philosophising have been most successfully applied.
FINIS.
* * * * *
Transcriber Note
Minor typos corrected. Some differences in application of accents and
formatting were left as printed.