165. In a region where the action of heat was accompanied with such

compression as is here supposed, there could be no fire, properly so

called, and no combustion; this is admitted by Dr Hutton, and it is

therefore a fallacious argument which is brought against his theory,

from the impossibility of fire being maintained in the bowels of the

earth. This impossibility is precisely what he supposes; and yet Mr

Kirwan's arguments are directed, not against the existence of heat in

the interior of the earth, but against the existence of burning and

inflammation.

After taking notice,[74] that Saussure had succeeded, though with

extreme difficulty, in melting a particle of limestone, so small as

to be visible only with a microscope, "what (adds he) must have been

the heat necessary to melt whole mountains of this matter? Judging

by all that we at present know of heat, such a high degree could

only be produced by the purest air, acting on an enormous quantity

of combustible matter. Now, EHRMAN observed, that the combustion of

two hundred and eighty cubic inches of air, acting on charcoal, was

not able to effect the fusion of one grain of Carrara marble; from

whence it is apparent, that all the air in the atmosphere, nor in ten

atmospheres, would not melt a single mountain of this substance, of

any extent, even if there were a sufficient quantity of inflammable

matter for it to act upon. Judging also of subterraneous heat by what

we know of that of volcanoes, no such heat exists: the highest they

in general produce, is that requisite for the fusion of the volcanic

glass called obsidian, which Saussure found not to exceed 115° of

Wedgewood; but basaltine, which requires 140° of Wedgewood, is never

melted in the lavas of Ætna. How little capable, then, would volcanic

heat be to effect the fusion of Carrara marble, which, according to

the same excellent author, would require a heat of upwards of 6300°

of Wedgewood, if this pyrometer could extend so far? And in what

circumstances does Dr Hutton suppose this astonishing heat to have

existed, and even still to exist, under the ocean, in the bowels of

the earth, where neither a sufficient quantity of pure air, nor of

combustible matter, capable of such mighty effects, can, with any

appearance of probability, be supposed to exist: and, without these,

such degrees of heat cannot even be imagined, without flying into the

region of chimeras."

[Footnote 74: Geol. Essays, p. 453.]

166. Now, this reasoning is not applicable to Dr Hutton's hypothesis

of subterraneous heat, because it is grounded on experiments, where

that very separation of the volatile and fixed parts takes place, which

is excluded in that hypothesis. When limestone or marble is exposed

to such heat as is here mentioned, or even to heat of a degree vastly

inferior, the carbonic gas is expelled, and the body is reduced to pure

lime; from the refractory nature of which, as we learn from the fact

relative to barytes, mentioned above, no conclusion can be drawn as to

the infusibility of the same substance, when combined with the carbonic

gas. The Carrara marble may require a heat of 6300° of Wedgewood, to

melt it in the open air, where the carbonic gas escapes from it; but

under such a pressure as would retain this gas, it cannot be inferred,

that it might not melt with the heat of a glass-house furnace. In like

manner, it may be true, that two hundred and eighty cubic inches of

air, acting on charcoal, cannot effect the fusion of one grain of this

marble, after its fixed air is driven off from it; but we cannot from

thence draw any inference, applicable to a case where the carbonic gas

is retained, and where the action of heat is independent of atmospheric

air.

Nothing, therefore, can be more inconclusive than this reasoning,

as it proceeds on the supposition, that Dr Hutton's system admits

propositions, which in fact it expressly denies.

167. Of the production and maintenance of heat, in circumstances

so different from those of ordinary experience, we can hardly be

expected to give any explanation; but we are not entitled, merely

on that account, to doubt of the existence of such heat. Mr Kirwan

thinks otherwise: "Judging," he says, "from all we at present know of

heat, such a high degree of it, (as will melt limestone,) could only

be produced by the purest air, acting on an enormous quantity of

combustible matter. Without these, such degrees of heat cannot even be

imagined, without flying into the region of chimeras."[75]

[Footnote 75: Geol. Essays, p. 454.]

Now, in the first place, the high degree of temperature which is

here understood, is probably not necessary to the purposes of

mineralization, as has just been shown; and, in the second place, it is

not FIRE, in the usual sense of the word, but HEAT, which is required

for that purpose; and there is nothing chimerical in supposing, that

nature has the means of producing heat, even in a very great degree,

without the assistance of fuel or of vital air. Friction is a source

of heat, unlimited, for what we know, in its extent, and so perhaps

are other operations, both chemical and mechanical; nor are either

combustible substances, or vital air, concerned in the heat thus

produced. So also the heat of the sun's rays in the focus of a burning

glass, the most intense that is known, is independent of the substances

just mentioned; and, though that heat certainly could not calcine a

metal, nor even burn a piece of wood, without oxygenous gas, it would

doubtless produce as high a temperature in the absence as in the

presence of that gas.

It is true, that it is not by the solar rays that subterraneous heat

is produced; but still, from this instance, we see, that there is no

incongruity in supposing the production of heat to be independent of

combustible bodies, and of vital air. We are indeed, in all cases,

strangers to the origin of heat; philosophers dispute, at this moment,

concerning the source of that which is produced by burning; and much

more are they at a loss to determine, what upholds the light and heat

of the great luminary, which animates all nature by its influence. If

we would form any opinion on this object, we shall do well to attend

to the suggestions of that great philosopher, who was hardly less from

others by his doubts and conjectures, than by his most rigorous and

profound investigations. "May not great, dense, and fixed bodies, when

heated beyond a certain degree, emit light so copiously, as, by the

emission and reaction of its light, and the reflections and refractions

of its rays within its pores, to grow still hotter, till it comes to

a certain period of heat, such as is that of the sun? And, are not

the sun and fixed stars great earths, vehemently hot, whose heat is

conserved by the greatness of the bodies, and the mutual action and

reaction between them and the light which they emit?"[76]

[Footnote 76: Newton's Optics, _ubi supra_.]

168. Some recent experiments, seem to make the suggestions in this

query applicable to an opaque body like the earth, as well as to

luminous bodies, such as the sun and fixed stars. The radiation of

heat, where there is no light, was first rendered probable by the

experiments of M. PICTET of Geneva;[77] and the only objections to

which the conclusions from those experiments seemed liable, are removed

by the late very important discoveries of Dr HERSCHEL.[78] From these

it appears, that heat is capable of refraction and reflection, as well

as light, so that it is not absurd to suppose, that _the heat of great,

dense, and faced bodies, may be conserved by the greatness of the

bodies, and the mutual action and reaction between them and the heat

which they emit_.

[Footnote 77: Essai sur le Feu.]

[Footnote 78: Phil. Trans. 1800, p. 84.]

The existence of subterraneous heat is still further rendered probable

from the researches of MAIRAN, which tend to show, that there is

another source of terrestrial heat besides the influence of the solar

rays.[79]

[Footnote 79: Mém. de l'Acad. des Sciences, 1765, p. 143.]

Whatever be the truth with regard to these conjectures, it is certain,

that the first and original source of heat is independent of burning.

Burning is an _effect_ of the concentration of heat; and though, by a

certain reaction, it has the power of continuing and augmenting that

heat, it never can be regarded as its primary and material cause. When,

therefore, we suppose a source of heat, independent of fire and of

burning, we suppose what certainly exists in nature, though we are not

informed of the manner of its existence, nor of its place, otherwise

than from considering the phenomena of the mineral kingdom.

169. Lastly, we are not entitled, according to any rules of

philosophical investigation, to reject a principle, to which we are

fairly led by an induction from facts, merely because we cannot give

a satisfactory explanation of it. It would be a very unsound view of

physical science, which would induce one to deny the principle of

gravitation, though he cannot explain it, or even though the admission

of it reduces him to great metaphysical difficulties. If indeed a

downright absurdity, or inconsistency with known and established

facts, be involved in any principle, it ought not to be admitted,

however it may seem calculated to explain other appearances. If, for

instance, Dr Hutton held, that combustion was carried on in a region

where there was no vital air, we should have said, that he admitted

an absurdity, and that a theory founded on such _postulata_ was worse

than chimerical. But, if the only thing imputable to him is, that,

being led by induction to admit the fusion of mineral substances in the

bowels of the earth, he has assumed the existence of such heat as was

sufficient for this fusion, though he is unable to assign the cause

of it, I believe it will be found, that his system only shares in an

imperfection, which is common to all physical theories, and which the

utmost improvement of science will never completely remove.

170. Thus, then, we are led, it must be allowed, into the _region of

hypothesis_ and conjecture, but by no means into that of chimeras.

Indeed, the reproach of flying into the latter region, may be said to

come but ill from one, who has trode so often the crude consistence of

the chaos, and who delights to dwell beyond the boundaries of nature.

By sojourning there long, it is not impossible that the eye may become

so accustomed to fantastic forms, that the figures and proportions of

nature shall appear to it deformed and monstrous.

NOTE VIII. § 24.

_Sparry structure of

calcareous petrifactions._

171. When the shells and corals in limestone are quoted by

mineralogists, it is not always considered in what state they are

found. In general, they have a sparry structure, very different

from that of the original shell or coral, of which, however, they

retain the figure with wonderful exactness, though probably sometimes

altered in size. Though sparry, they are often foliated, and preserve

their animal, in conjunction with their mineral, texture. Now, this

crystallization is a mark of some operation, quite different from any

that can be ascribed to the water in which these bodies had their

origin, and by which they were brought into their place. They were

impervious to water; and it cannot be said that their sparry structure

has been derived from the percolation of that fluid, carrying new

calcareous matter into their pores. We can account for the change

produced in them, I think, only by supposing them to have been softened

by heat, so as to permit their parts to arrange selves anew, and to

assume the characteristic organization of mineral substances.

All shells have not the change effected on them that is here referred

to; those in chalk, for instance, retain very much their original form

in all respects. This is what we might expect from the very different

degree of intensity, with which the mineralizing cause has acted on

chalk, and on limestone or marble. In general, it is in the hardest

and most consolidated limestone, that the marine objects are most

completely changed into spar.

It would be exceedingly interesting to examine, whether any of the

phosphoric acid remains united to shells of either of these kinds. We

might most readily expect it to be united, in a certain degree, to the

shells that are least mineralized.

This experiment would enable us also to appreciate the force of Mr

Kirwan's argument against the finer marbles, such as the Carrara,

containing shells.[80] This argument proceeds on an experiment,

mentioned in the _Turin Memoirs_ for 1789, from which it appears,

that no phosphoric acid is found in pure limestone; and its absence,

Mr Kirwan says, cannot be attributed to fusion, as phosphoric acid is

indestructible by heat.

[Footnote 80: Geol. Essays, p. 458.]

He calls this a demonstration; but, in order to entitle it to that

name, it will be necessary, first, to prove, that phosphoric acid

exists in those limestones which evidently consist of shells in a

mineralized state. If these are found without phosphoric acid, it is

evident that the preceding argument fails entirely. If they are found

to contain that acid, it will then no doubt afford a probability,

though not a demonstration, that Carrara marble does not directly

originate from shells.

That nature has some process, by which the above acid is separated

from the earth of bones, and probably also from the earth of shells,

is evident from the state in which the bones are found in the caves of

Bayreuth. Those that are the most recent, and least petrified, contain

most of the phosphoric acid. Where the petrifaction has proceeded far,

that acid is not found.

172. Among many of the strata, such a fluidity has prevailed, as

to enable some of the substances included in them to crystallize.

Calcareous spar and siliceous crystals are often found in stratified

rocks, forming veins of secretion, or lining close cavities, included

on all sides by the uncrystallized rock. In the instances of gneiss,

and many species of marble, almost the whole matter of the stratum is

crystallized. This union of a stratified and crystallized structure

in the same substance, has a great affinity to that union of the

crystallized with the organic structure of shells and corals which has

just been mentioned; and both are doubtless to be referred to the same

cause.

NOTE IX. § 81.

_Petroleum, &c._

173. According to the theory of coal laid down above, its two chief

materials, charcoal and bitumen, being furnished by the vegetable and

animal kingdoms, both of the land and of the sea, have formed with one

another a new combination, by the action of subterraneous heat; but

have also, in some cases, been separated by that same action, where

the degree of compression necessary for their union, happened to be

wanting. The carbonic part, when thus separated from the bituminous,

forms an infusible coal, which burns without flame: the bituminous

part, when separated from the carbonic, is found in the various states

of naphtha, petroleum, asphaltes, and jet.

The great resemblance of infusible or blind coal, to the residuum

obtained by the distillation of bituminous coal; and again, the

coincidence of the bitumens just named, with the volatile part, or

the matter brought over by such distillation, are strong arguments

in favour of this theory. The other facts in the natural history of

coal, serve to confirm the same conclusion; but it must be confessed,

that what we know of the pure bitumens, except the circumstance

just mentioned, is of a more ambiguous nature, and may be reconciled

with different theories. The drops of petroleum contained within the

cavities of the limestone, mentioned at § 31, are however strong facts

in confirmation of Dr Hutton's opinions, and they are furnished by the

substances purely bituminous. A careful examination would probably

make us acquainted with others of the same kind, for limestone is very

often the matrix in which petroleum and asphaltes are contained. The

greatest mine of asphaltes in Europe, that in the _Val de Travers_ in

the territory of Neufchâtel, is in limestone, from which, though it in

some places exudes, it is in general extracted by the application of

heat. The strata for several leagues are impregnated with bitumen; and,

if examined with attention, would probably afford specimens similar to

those which have just been mentioned.

174. It is a general remark, that, where petroleum is found, on

digging deeper, they come to asphaltes; and, at a depth still greater,

they discover coal. This probably does not hold invariably; but

it is certain, that most of the fountains of petroleum are in the

neighbourhood of coal strata. Petroleum and asphaltes are found in

great abundance in Alsace, in a bed of sand, between two beds of clay

or argillaceous schistus, and the same country also affords coal.[81]

This is true likewise of the fossil pitch of Coal-Brookdale; and of the

petroleum found in St Catharine's Well, near Edinburgh. Auvergne[82]

contains abundance of fossil pitch, which exudes, in the warm season,

from a rock impregnated with it through its whole mass. There are also

coal strata in the same country, not far distant.

[Footnote 81: Encyclopédia, mot, _Asphalte_.]

[Footnote 82: Voyage en Auvergne, par Lagrand, tom. i. p. 351.]

A very satisfactory observation relating to this subject, has lately

been communicated from a country, with whose natural history we were

till of late entirely unacquainted. In the Burmha empire, petroleum is

dug up in an argillaceous earth, from the depth of seventy cubits. This

argillaceous earth, or schistus, lies under a bed of freestone; and

under all, about one hundred and thirty cubits from the surface, is a

bed of coal.[83]

[Footnote 83: Asiatic Researches, vol. vi, art. 6. p. 130.]

175. In the petroleum lake of the Island of Trinidad, described _Phil

Trans._ 1789, the petroleum evidently exudes from the rock, and is

collected in a variety of springs in the bottom, after which it

hardens, and acquires the consistency of pitch. The manner, therefore,

in which petroleum exists in the strata, is very consistent with the

idea of its having been introduced in the form of a hot vapour.

Even amber appears to have some relation to coal. It is found in the

unconsolidated earth in Prussia and Pomerania; but I am not sure

whether this earth is _travelled_ or not. In the same earth where the

amber is found, there is often a mixture of coaly matter, which burns

in the fire; it is apparently fibrous, and has been considered as a

kind of fossil-wood.[84]

[Footnote 84: Buffon, Hist. Nat. des Mineraux, tom. ii. p. 5.]

These circumstances make out a connection between the purer bitumens

and ordinary coal; but do not, it must be acknowledged, establish any

thing with respect to the more immediate relation, supposed in this

theory to exist between them and blind coal. It is probable, indeed,

that, to discover any facts of that kind, the natural history of both

substances must be more carefully examined; the natural history of

blind coal, in particular, has hitherto been but little attended to.

176. A fact is mentioned by Mr Kirwan, which must not be regarded as

less valuable for being adverse to this theory. It is, that neither

petroleum, nor any fossil bitumen, is found in the vicinity of the

Kilkenny coal, as might be expected, if that coal was deprived of

its bituminous part by subterraneous distillation.[85] This, however,

admits of explanation. Though a general connection, on the above

hypothesis, might be expected between bitumens and infusible coal, we

cannot look for it in every instance. The heat which drove off the

bitumen from one part of a stratum of coal, may only have forced it to

a colder part of the same stratum; and thus, in separating it from one

portion of carbonic matter, may have united it to another. Blind coal

may therefore be found where no bitumen has been actually extricated.

In like manner, bitumen may have been separated, where the coal was

not reduced to the state of coke, as a part of the bitumen only may

have been driven off, and enough left to prevent the coal from becoming

absolutely infusible.

[Footnote 85: Geol. Essays, p. 473.]

It should be considered too, if the bitumen was really separated, and

forced, in the state of vapour, into some argillaceous or limestone

stratum, that this stratum may have been wasted and worn away long ago,

so that the bitumen it contained may have entirely disappeared. It does

not therefore necessarily follow, that, wherever we find blind coal,

there also we should discover some of the purer bitumens.

NOTE X. § 37.

_The height above the level of the sea

at which the marks of aqueous

deposition are now found._

177. We have two methods of determining the _minimum_ of the change

which has happened to the relative level of the sea and land; or

for fixing a limit, which the true quantity of that change must

necessarily exceed. The one is, by observing to what height the regular

stratification of mountains reaches above the present level of the sea;

the other is, by determining the greatest height above that level,

at which the remains of marine animals are now found. Of these two

criteria, the first seems preferable, as the fact on which it proceeds

is most general, and least subject to be affected by accidental causes,

or such as have operated since the formation of the rocks. The results

of both, however, if we are careful to select the extreme cases, agree

more nearly than could have been expected.

178. The mountain Rosa, in the Alps, is entirely of stratified rocks,

very regularly disposed, and nearly horizontal.[86] The highest summit

of this mountain is, by Saussure's measurement, 2430 toises, or 14739

English feet, above the level of the sea, or lower than the top of

Mont Blanc only by 20 toises, or 128 feet.[87] This is, I believe, the

highest point on the earth's surface, at which the marks of regular

stratification are certainly known to exist; for though, by the account

of the same excellent mineralogist, Mont Blanc itself is stratified,

yet, as the rock is granite, the stratification vertical, and somewhat

ambiguous, it is much less proper than Monte Rosa for ascertaining the

limit in question.

[Footnote 86: Voyages aux Alpes, tom. iv. § 2138.]

[Footnote 87: _Ibid._ § 2135.]

179. Again, in the new continent, we have an instance of shells

contained in a rock, not much lower than the summit of Monte Rosa.

This is one described by Don ULLOA, near the quicksilver mine of

Guanca-Velica, in Peru. The height at which a specimen of these shells,

given by Ulloa to M. Le GENTIL, was found, was 2222 1/3 toises, or

14190 feet English, above the level of the seas.[88] This height agrees

with the preceding, within 549 feet, a quantity comparatively small.

[Footnote 88: See Hist. Acad. des Sciences, 1770. Phys. Générale, No.

7.]

180. The last of the facts just mentioned is curiously commented on by

Mr Kirwan. As he has proved, he says, that the mountains higher than

8500 feet were all formed before the creation of fish, it follows,

that the shells found at Guanca-Velica, must have been carried there

by the deluge.[89] Now, without objecting to the proof here referred

to, (though it seems very open to objection,) it is sufficient to

remark, that, if the shells at Guanca-Velica were carried there by

the deluge, or any other cause that operated after the formation of

the rock of which the mountain consists, they can make no part of

that rock, but must lie, like other adventitious fossils, loose and

detached on the surface, or at most externally agglutinated to the

stone. This, however, is certainly not the fact; for, in the account

just quoted, we read, that Don Ulloa told M. le Gentil, "qu'il avoit

détaché ces coquilles d'un banc fort épais." This seems plainly to

indicate, that the shells were included in a bed of rock; But, granting

that the expression is a little ambiguous, on turning to the _Mémoires

Philosophiques_ of the same author, the difficulty is completely

removed, and it is made evident, that these shells are in fact

integrant parts of the rock. "On voit dans ces montagnes-là, (about

Guanca-Velica, and particularly at that in which is the quicksilver

mine,) des coquilles entières, petrifiées et enfermées au milieu de la

roche, que les eaux de pluie mettent à decouvert. Ces coquilles font

corps avec la pierre; mais malgré cela, on remarque que la partie qui

fut coquille, se distingue par la couleur, la structure, la qualité de

la matière de tout autre corps pierreux qui l'enferme, et du massif qui

s'est fixé entre les deux ecailles,"[90] &c. He goes on to say, that

one can distinguish marks of these shells having been worn, before they

were included in the stone.

[Footnote 89: Geol. Essays, p. 54.]

[Footnote 90: Mém. Philosophiques de Don Ulloa, Discours xvi. vol. i.

p. 364.]

181. Thus it appears, that whatever proof any fossil shell affords,

that the rock in which it is found was formed under the sea, the

same is afforded by the fossil shells of Guanca-Velica; and we are,

therefore, perfectly entitled to conclude, that the relative level of

the sea and land has changed, since the formation of the latter, by

more than 14000 feet. The height assumed in § 37 is therefore much

under the truth; and the water, for which the Neptunists must provide

room in subterraneous caverns, might very well have been stated at

more than a five-hundredth part of the whole mass of the earth.

Thus also the argument by which the Neptunists would connect the

creation of fish with the beginning of the secondary mountains, falls

entirely to the ground. Indeed, it is strange that Mr Kirwan should

have supposed it possible, that the shells in question were loose and

unconnected with the rock, and had continued so, ever since the deluge,

in such elevated ground, where the torrents wear and cut down the

mountains with unexampled violence, and have hollowed out _Quebradas_

so much deeper and more abrupt than the glens or vallies among other

mountains. He had not, I believe, seen the passage I have quoted from

Ulloa; but the circumstances did not warrant the shells in question to

be regarded as extraneous and adventitious fossils. A geologist should

have known better than to suppose this possible. When we see VOLTAIRE

ascribing to accidental causes the transportation of those shells

which he had been told were often found among the Alps, we can excuse

in a Poet and a Wit, that ignorance of the facts in mineralogy, which

concealed from him the extreme absurdity of his assertion; but when a

Chemist or Mineralogist talks and reasons in the same manner, we cannot

consider him as entitled to the same indulgence.

NOTE XI. § 42.

_Fracture and dislocation

of the strata._

182. The greatest part of the facts relative to the fracture and

dislocation of the strata, belongs to the history of veins. The

instances of slips, where no new mineral substance is introduced

between the separated rocks, are what properly belong to this place.

The frequency of these, and their great extent, are well known wherever

mines have been wrought. In some of them no opening is left, but the

slipped strata remain contiguous; in other cases, there is introduced

an unconsolidated earth, often a clay, which may be supposed to have

come from above, arid very probably to have been carried down by the

water. In some such cases, however, there are not wanting appearances,

which show the matter in the slip to have been forced up from below,

as we find it to contain substances which could not have come from the

surface.[91]

[Footnote 91: Unconsolidated earth contained between the sides of

a rock that has slipped, is frequent in Cornwall, and is called a

_Fleukan_. ]

183. A very remarkable fact of this kind occurred not long ago, in

digging the Huddersfield canal in Yorkshire; and a very distinct

account of it is given in the _Philosophical Transactions_, by the

engineer who directed the work. In carrying a tunnel into the heart of

a hill, the miners came to what is called in the description a _fault_,

_throw_, or _break_, or what we have here called a shift, which was

filled with _shale_ set on edge, mixed with softer earth, and in some

places with small lumps of coal. The fault or space filled with these

materials, was in general about four yards broad, and lay nearly in

the direction of the tunnel, so that a considerable extent of it was

visible. Beside the shale, it contained a _rib_ of limestone, about

four feet thick, which run parallel to the sides of the _fault_, and

about four feet from the southern margin of it. On each side of this

rib were found balls of limestone, promiscuously scattered, and of

various sizes, from an ounce to one hundred pounds weight. The balls,

when broken, were found to contain some pyrites near their edges; they

were not perfectly globular, but flattened on the opposite sides, and

similar to one another.[92] At the time when the account was written,

about seventy yards of the rib had been discovered.

[Footnote 92: Phil. Trans. 1796, p. 350.]

184. Now, it is certain, that neither this rib of limestone, nor the

balls that accompanied it, can have come from above, as there is no

limestone within twenty miles of the place where they were found. They

must, therefore, have been forced up from below, and no doubt belong

to some limestone strata, which lie there at a great depth under the

surface. The length of this fragment of rock, which, from the account,

one must suppose to have been entire, conveys no mean idea, either of

the intensity or regularity of the force by which it was brought into

its present situation. In veins, it is not uncommon to meet with stones

that appear to have come from a greater depth: but this is probably the

most remarkable instance of the same phenomenon, which has appeared in

a mere slip, and none, I think, can speak a language less liable to be

misunderstood.

185. I shall here mention another mark of violent fracture, that has

been observed in rocks of breccia or pudding-stone, which, though not

of the same kind with the preceding, and of a nature quite peculiar,

belongs rather to this place than any other. In rocks of the kind,

just mentioned, it sometimes happens, that considerable portions are

separated from one another, as if by a mathematical plane, which had

cut right across all the quartzy pebbles in its way. None of the

pebbles are drawn out of their sockets, that is, out of the cement that

surrounds them, but are divided in two with a very smooth and even

fracture. The pebbles, in the instances which I have seen, were of

quartz, and other species of primary and much indurated rock.

Lord WEBB SEYMOUR and I observed pudding-stone rocks, exhibiting,

instances of this singular kind of fracture, near Oban, in Argyleshire,

about three years ago. The phenomenon was then entirely new to us both;

but I have since met with an instance of the same kind in Saussure's

last work. As the fact is of so particular a kind, I shall state it in

his own words: The place was on the sea shore, near the little town of

Alassio, between Nice and Genoa.

"En passant entre ces blocs de breche, j'admirai quelques-uns

d'entr'eux, d'une grandeur considérable, et taillés en cubes, avec

la plus parfaite régularité. Il y avoit ceci de remarquable, c'est

que l'action de la pesanteur, qui avoit taillé ces cubes en rompant

leurs couches, avoit coupé tous les cailloux des breches à fleur de

la surface de la pierre, aussi nettement que si c'eût été une masse

molle qu'on eût tranchée verticalement avec un rasoir. Cependant parmi

ces cailloux, la plupart calcaires, il s'en trouvoit de très durs, de

petrosilex, par exemple, même de jade, qui étoient tranchées tout

aussi nettement que les autres."[93]

[Footnote 93: Voyages aux Alpes, tom. iii. § 1731.]

186. This description is no doubt accurate, though it involves in it

something of theory, viz. that the fracture was made by the weight of

the stone. This may indeed be true: the operation probably belongs

altogether to the surface, and is one with which the powers of the

mineral regions are not directly concerned. The phenomenon, however,

appears to me, on every supposition, very difficult to explain. In the

specimen which I brought from Oban, the smallest pieces of stone are

cut in two, as well as the largest. The consolidation and hardness of

the mass are very great, and the connection of the different fragments

so perfect, that it is no wonder the whole should break as one stone.

But still, that the fracture should be so exactly in one plane, and

without any shattering, is not a little enigmatical; if it is indeed

a fracture, it must be the consequence of an immense impulse, very

suddenly communicated.

NOTE XII. § 43.

_Elevation and inflection

of the strata._

187. The evidence of the different formation of the primary and

secondary strata, and of the changes which the former have undergone,

is best seen at the points where those strata come into contact with

one another. Dr Hutton was not the first who observed these junctions,

though the first who rightly interpreted the appearances which they

exhibit. He has mentioned observations of this sort by De Luc on the

confines of the Hartz; by the author of the _Tableau de la Suisse_,

at the pass of Yetz; by Voight, in Thuringia; and Schreiber, at the

mountain of Gardette.[94]

[Footnote 94: Theory of the Earth, vol. i. p. 410 to 453.]

The leading facts to be remarked, are,

I. The vertical or very upright position of the primary or lower strata.

II. The superstratification of the secondary, in a position nearly

horizontal, so as to be at right angles to those on which they rest.

III. The interposition of a breccia between them or, as happens in

many cases, the transition of the lowest of the secondary beds into a

breccia, containing fragments sometimes worn, sometimes angular, of the

primary rock.

This last is a phenomenon extremely general, and all our subsequent

information confirms Dr Hutton's anticipations concerning it. "It will

be very remarkable," he says, "if similar appearances, (such as those

of the breccia described by Voight,) are always found upon the junction

of the Alpine with the level countries."[95] Saussure, in a part of his

work, not published when Dr Hutton wrote this passage, has attested the

generality of the fact with respect to the whole Alps, from the Tyrol

to the Mediterranean: "Un sait que l'on observe sans aucune exception,

ce sont les amas de débris, sous la forme de blocs, de breches, de

poudingues, de grès, de sable, ou amoncelés, et formant des montagnes,

ou des collines, dispersés sur le bord exterieur, ou même dans les

plaines qui bordent la chaine des Alpes."[96]

[Footnote 95: Theory of the Earth, vol. i. p. 448.]

[Footnote 96: Voyages aux Alpes, tom. iv. § 2330.]

This passage is perfectly decisive as to the generality of the fact,

that the Alps, from the Tyrol to the Mediterranean, are bordered all

round by pudding-stones or breccias. At the same time, it is necessary

to remark, that M. Saussure, by enumerating loose blocks and sand,

along with pudding-stones, breccias and grit, confounds together things

which are extremely different, and which have had their origin at

periods extremely remote from one another. The consolidated rocks of

breccia, pudding-stone and grit, though they are indications of waste,

have received their present character at the bottom of the sea: the

loose blocks of stone, the sand and gravel, on the other hand, are the

effects of the waste now going forward on the surface of the land, and

are the materials out of which rocks of the three kinds just mentioned

may hereafter be composed. If so skilful a mineralogist as Saussure

is guilty of such inaccuracy, it must be ascribed to the confusion

necessarily arising from the system which he followed, and not to his

own want of discrimination.

188. The same phenomenon, of a breccia circumscribing the primary

mountains, is met with in Scotland; and the Grampians, wherever they

are bounded by secondary strata, whether on the south or north, afford

examples of it. The breccia generally consists of the fragments of

the primary rock, most commonly rounded, but sometimes also angular,

united by a cement of secondary formation, and the whole disposed

in horizontal beds. It was on the constancy of this accompaniment

of the primary strata, and on the great quantity of highly polished

gravel often included in these breccias, that Dr Hutton grounded the

hypothesis of the double raising up and letting down of the ancient

strata. See § 43.

189. As the spots where the primary and secondary rocks may be seen

in contact with one another are of great importance in geology, and

present to the senses the most striking monuments of the high antiquity

and great revolutions of the globe, it may be useful to point out such

of them as have been observed in this island. To those which Dr Hutton

has described, I have a few more to add, the result of some geological

excursions, which I made in company with the Right Honourable Lord

WEBB SEYMOUR, to whose assistance I have been much indebted in the

prosecution of these inquiries.

190. The most southern junction which we observed is at Torbay, where

the ancient schistus which prevails along the coast, from the Land's

End to that point, receives a covering of red horizontal sandstone,

the same which composes the greater part of Devonshire. The spot where

the immediate contact is visible, is on the shore, a little to the

south of Paynton; and one circumstance, which among many others serves

to distinguish the different formation of the two kinds of rock, is,

that the schistus, which is elevated here at an angle of about 45°, is

full of quartz veins, which veins are entirely confined to it, and do

not, in as far as we could observe, penetrate into the sandstone, in a

single instance. It is probable, that on the north shore of the bay,

the same line of junction is visible: we saw it at Babicomb Bay, still

more to the northward.

191. From this place, the secondary strata of different kinds prevail

without interruption, along the coast of the British Channel, and

of the German Ocean, as far as Berwick upon Tweed, and for some

miles beyond it. The sea coast then intersects a primary ridge, the

Lammermuir Hills, which traverses Scotland from east to west, uniting,

near the centre of the country, with the metalliferous range of

Leadhills, and afterwards with the mountains of Galloway. The section

which the sea coast makes of the eastern extremity of this ridge, is

highly instructive, from the great disturbance of the primary strata,

and the variety of their inflections. The junction of these strata

with the secondary, on the south side, is near the little sea-port of

Eyemouth, but the immediate contact is not visible.

On the north side of the ridge, the junction is at a point called the

_Siccar_, not far from Dunglass, the seat of Sir James Hall, Baronet.

By being well laid open, and dissected by the working of the sea,

the rock here displays the relation between the two orders of strata

to great advantage. Dr Hutton himself has described this junction;

_Theory of the Earth_, vol. i. p. 464.

192. From the point just mentioned, the secondary strata continue as

far as Stonehaven, where the southern chain of the Grampian mountains

is intersected by the sea-coast. Here a great mass of pudding-stone

appears to lie on the primary strata, but their immediate contact has

not been observed.

193. Going along the coast toward the north, the next junctions which

we saw were on the shore, one near Gardenston, and another near Cullen,

in Banffshire. The latter is very distinct; it is about a mile to the

westward of the rocks called _The Three Kings_, where a red sandstone,

the lower beds of which involve much quartzy gravel, lies horizontally

upon very regular, upright, and highly indurated strata. Some of these

strata are micaceous, and others of the granulated quartz, mentioned in

§ 153.

194. This last is, I believe, the most northern junction which has

been observed in our island. The western coast furnishes several more,

which however are not all visible. The line of separation, between

the primary schistus of the Grampians and the sandstone which covers

it, is intersected at its western extremity by the Frith of Clyde,

not far from Ardencaple in Dunbartonshire. The two kinds of stone can

be traced within a few yards of each other, but not to the actual

contact: the beds of sandstone nearest the schistus form as usual a

breccia, loaded with fragments of the primary rock. The secondary rock,

which begins here, continues for about fifty miles south, to Girvan in

Ayrshire, where the primary schistus again rises up, but is not seen in

contact with the secondary. It extends to the Mull of Galloway and the

shores of the Solway Frith.

The Isle of Arran, however, not far distant from this part of the

coast, contains a junction at its northern extremity, where secondary

strata of limestone lie immediately on a primary micaceous schistus.

This is described by Dr Hutton, and was the first phenomenon of the

kind which he had an opportunity of examining.[97] The junction is

visible but at one spot, and is not seen so distinctly as in some of

the instances just mentioned; but the great quantity of pudding-stone

near it, renders it more interesting than it would be otherwise. As the

greater part of this little island is surrounded by secondary strata,

other junctions might be expected to be visible.

[Footnote 97: Theory of the Earth, vol. i. p. 429.]

195. On the coast of England and Wales, from the Solway Frith to the

Land's End, though there are several alternations from secondary to

primary strata, I know not that any of them have been observed. At St

Bride's Bay, in Pembrokeshire, the primary and secondary strata are

seen very near their junction; but the precise line I believe is not

visible. The coal-pits in the secondary strata, approach here within a

few hundred yards of the primary. The secondary strata which commence

at this place, occupy both sides of the Bristol Channel, and meet the

Cornish schistus, which extends across the north of Devonshire to the

Quantock Hills, in a line that may be looked for on the sea coast, some

where between Watchett and Minehead.

196. Besides the sea coast, the beds of rivers may be expected to

afford information on this subject. To the instances I have mentioned,

I have accordingly two others from the inland country to be added. One

of them is from the river Jed, a little way above Jedburgh, where the

secondary strata are seen lying horizontally on the primary, a section

of both being made by the bed of the river. The phenomena here are very

distinct, and strongly marked; Dr Hutton has described and represented

them in a plate.[98] He has mentioned another junction, not far from

this, which he saw in the Tiviot. Both these belong to the same primary

ridge with the Siccar point.

[Footnote 98: Theory of the Earth, vol. i. p. 430; also plate 3.]

197. I shall mention only one other, which was discovered by Lord Webb

Seymour and myself, at the foot of the high mountain of Ingleborough,

in Yorkshire. As we went along the Askrig road from Ingleton, about a

mile and a half from the latter, an opening appeared in the side of

the hill, on the right, about one hundred yards from the road, formed

by a large stone, which lay horizontally, and was supported by two

others, standing upright. On going up to the spot, we found it was the

mouth of a small cave, the stone lying horizontally, being part of a

limestone bed, and the two upright stones, vertical plates of a primary

argillaceous schistus. The limestone bed, which formed the roof of the

cave, was nearly horizontal, declining to the south-east; the schistus

nearly vertical, stretching from north-west by west, to south-east by

east. The schistus, though close in contact with the limestone, seemed

to contain nothing calcareous, and did not effervesce with acids in the

slightest degree.

As this cave is at the foot of Ingleborough, a cold wind, 24° below the

temperature of the external air, which issued from the mouth of it,

might very well be supposed to come from the inmost recesses of that

mountain. Ingleborough, which consists entirely of strata of limestone

and grit, nearly horizontal, and alternating with one another, rises

to the height of 1800 or 2000 feet above the spot where we now stood.

This, I believe, is the greatest thickness of secondary strata that

has ever been observed incumbent on the primary, and it is therefore

a geological fact highly deserving of attention. The country all

round, to a very great extent, is composed of limestone, with a few

beds of grit interposed, and forming, beside Ingleborough, some other

high mountains, such as Wharnside and Pennigant, all resting, it is

probable, on the same foundation.

At the spot just described, no breccia appeared to be interposed

between the primitive and secondary rock; but we found a breccia at

another point of the same junction, not far distant. This was at a

cascade, in the river Greta, called Thornton Force, about two miles

and a half from the place just mentioned. The Greta here precipitates

itself from a horizontal rock of limestone; and, after a fall of

about eighteen or twenty feet, is received into a bason which it has

worked out in the primary schistus. This schistus is in beds almost

perpendicular; it exactly resembles that which has Just been described,

and stretches nearly in the same direction. On the south side of the

river a breccia was seen, lying upon the schistus, or rather, it might

be said, that the lowest beds of limestone contained in them many

rounded fragments of stone, which, on comparison, resembled exactly

the schistus underneath. The primary rock itself is here seven or eight

hundred feet above the level of the sea.

The same schistus, somewhat lower down the valley, and nearer to

Ingleton, appears in large quantities, and is quarried for slate. Here,

however, the immediate junction of the limestone and schistus does not

appear.

I have dwelt longer on the description of these appearances than on

any others of the same kind, because, from the great mass of secondary

strata which here covers the primary, the circumstances are such as we

cannot expect to see very often exemplified.

198. The Lakes of Cumberland are much visited by travellers; and it may

be worth remarking, on that account, that, as the site of these lakes

is a patch of primary country, bounded on all sides by secondary, so,

in the rivers that run from the lakes, such junctions as we are now

treating of may be expected to be found. Under Dun-Mallet, on the side

toward Ulles Water, we observed a breccia, which was in horizontal

layers, and seemed to lie on the primary schistus, so that the whole

hill is perhaps a piece of more indurated breccia, or secondary rock,

which has resisted the wearing and washing down of the rivers better

than the rest.

199. After ascertaining the fact of the disturbance of the strata, and

their removal from their original position, it is of consequence to

inquire into the direction of the force by which these changes have

been produced. Now, if the disturbed or elevated strata, were every

where in planes, without bending or sinuosity, it might perhaps be

hard to determine, whether that force had acted in the direction of

gravity, or in the opposite. Either supposition would account for the

appearances; and, as gravity is a known force, providing we can find

some place fit to receive the matter impelled downward by it, its

action would furnish the most probable solution of the difficulty.

It is on this principle that the Neptunian system proceeds, imagining,

that certain great caverns or vacuities having been opened in the

interior of the globe, a great part of the waters which formerly

covered its surface, retired into them, and much of the solid rock also

sunk down at the same time. In this way, one extremity of a stratum

has been elevated, while the other has been depressed, and a certain

inclination to the horizon has been given to the whole of it. Thus one

cause serves two purposes; the vacuities in the interior of the earth

account, both for the depression of the sea, and the elevation of the

land; and the Neptunists, if the phenomena were all such as have been

now stated, might boast of a felicity of explanation, not very usual in

their system.

But this appearance of success vanishes, when the elevation and

disturbance of the strata are more minutely examined, and are found

to include waving and inflection, in a great variety of forms. It

then becomes evident, that the beds of rock, at the time when they

were disturbed from their horizontal position, had not their present

hardness and rigidity, but were, in a certain degree at least, soft

and flexible. Without these qualities, they could not have received,

as they have often done, the curvature of a circle, not many feet,

nay, not many inches, in diameter; nor could they have been bent into

superficies, with their curvature in opposite directions, so that

the same surface is in one part convex, and in another concave, on

the same side, with a line of contrary flexure interposed. These are

appearances, not reconcilable with the mere falling in, and breaking

down of indurated rocks.

200. The inflections and wavings that we are here speaking of, though

not peculiar to the primary strata, are found most frequently among

them, and are perfectly familiar to every one who his travelled among

mountains with any view to the study of geology. The following are a

few instances of this phenomenon out of a great number which might be

produced.

Saussure, in describing the route from Geneva to Chamouni, mentions

many remarkable instances of the bending of the strata, and

particularly where the small stream of Nant d'Arpenaz forms a cascade,

by falling over the face of a perpendicular limestone rock. The strata

of this rock are bent into circular arches, extremely regular, and with

their concavity turned to the left. What deserves particularly to be

remarked, is, that a mountain behind the cascade has its strata bent

in a direction opposite to the former, or with their concavity to the

right. There is no doubt that the strata of both rocks are the same, so

that a vertical section of them would give a curve, in the figure of an

S.[99] These circumstances are mentioned by Saussure, and from them we

may infer this other property of these strata, that their section by a

horizontal plane, must exhibit a system of straight lines, probably all

parallel to one another.

[Footnote 99: Voyages aux Alpes, vol i. § 472; also, Theory of the

Earth, vol. ii. p. 30.]

The same mineralogist describes the calcareous strata which compose

the mountain Axenberg, on the side of the Lake of Lucerne, as having

from top to bottom of the mountain the form of the letter S compressed,

(_ecrasée_) with their curvature in some places very great. These

inflections are repeated several times, and often in contrary

directions; the layers are sometimes broken, where their curvature is

greatest.[100]

[Footnote 100: Voyages aux Alpes, tom. iv. § 1935.]

On the side of the same lake, is another instance of bent strata, in a

mountain, of which the beds are horizontal in the lower part, but are

bent at one end upwards, in the form of the letter C. The horizontal

part is of great extent, and the rock is also calcareous,[101]

[Footnote 101: _Ibid._ § 337.]

The Montagne de la Tuile, near Montmelian, receives its name from the

beds of rock being incurvated in form of a tyle.[102] Among secondary

mountains, the same kind of phenomena are observed, though less

frequently, and with less variety of inflection. The chain of Jura is

secondary, and the beds which compose it are of limestone, or of grit:

they are bent in such a manner, that in a transverse section of the

mountain, each layer would have the figure of a parabola.[103]

[Footnote 102: _Ibid._ vol. iii. § 1182, and plate i.]

[Footnote 103: _Ibid._ tom. i. § 334.]

201. The Pyrenees furnish abundance of phenomena of the same kind,

as we learn from the _Essai sur la Mineralogie des Pyrenées_. The

calcareous strata of the valley of Aspe, represented plate v. of that

work, deserve particularly to be remarked.

202. Our own island abounds with examples of the bending and inflection

of the strata, especially the primary, and many of them very much

resembling those in the Alps and Pyrenees. On the top of the mountain

of _Ben-Lawers_, in Perthshire, there is a rock, the face of which

exhibits a section of a great number of thin equidistant layers, bent

backwards and forwards like those described by Saussure; and this

unequivocal proof of the rock having once existed in the state of a

flexible and tenacious paste, is rendered more striking, by the great

elevation of the spot, and the ruggedness and induration, both of

the stone itself, and of every thing that surrounds it. Many other

mountains in this tract consist of a schistus, which is talcose rather

than micaceous, and subject, in a remarkable degree, to the sort of

sinuosity and inflection here treated of.

The appearances of the primary strata on the coast of Berwickshire,

have been already mentioned, as affording much valuable instruction in

geology. They also exemplify the waving and inflection of the strata

on a large scale, and with great variety. A section of some of them

is given by Dr Hutton, in his _Theory of the Earth_, vol. i. from a

drawing made by Sir James Hall. The nature of the curve superficies

into which the schistus is bent, is the better understood from this,

that, besides transverse sections from north to south, the deep

indentures which the sea has made, and the projecting points of rock,

exhibit many longitudinal sections, in a direction from east to west.

203. The dock-yards at Plymouth are in several places cut out of a

solid rock of primary schistus, singularly incurvated. The inflections

are seen there to great advantage, being exhibited in three sections,

at right angles to one another, transverse, longitudinal and horizontal.

204. From these instances, to which it were easy to add many more, two

conclusions may be drawn. The first of these is very obvious, viz.

that the strata must have been pliant and soft when they acquired

their present form. The bending of an indurated bed of stone into an

arch of great curvature, and without fracture, as in the preceding

examples, is a physical impossibility. Saussure has indeed observed a

fracture to accompany the bending, in one or two cases; but it is an

uncommon phenomenon, and, where it happens, must no doubt be understood

to indicate an imperfect flexibility. Now, if it be granted that the

strata were at any time soft and flexible, since their complete

formation, it will be found impossible to deny their having been

softened by the application of heat.

205. The second conclusion, alluded to above, results from a property,

which belongs very generally, if not universally, to the inflections of

the strata. This consists in their curvature being simple, or in one

dimension only, like a cylindric superficies, not double, or in two

dimensions, like the superficies of a sphere or spheroid. This may be

otherwise expressed by saying, that the sections of the bent strata,

by a horizontal plane, are straight lines, parallel to one another. On

this account, every such stratum seems as if it were bent over all axis

and the axes of all these different bendings, for a great extent of

country, are nearly parallel.

The truth of this is evident, where the strata are seen both

transversely and longitudinally. It holds remarkably of the primary

schistus on the coast of Berwickshire; where the beds of rock, if

cut transversely, by a vertical plane, exhibit the figures of very

complicated curves, with various maxima and minima, and points of

contrary flexure; but, if they are cut by a horizontal plane, the

section will produce nothing but straight lines, nearly parallel.

206. The constancy of the direction of the primary strata, when

estimated by their intersection with the horizontal plane, is often

very remarkable. Their elevation and flexure are subject to great and

sudden changes, so as to pass not only from greater to less, but from

one side to the opposite, within a small distance; but the horizontal

line in which they _stretch_, usually preserves the same bearing

to a great extent. The general direction of the primary strata, in

the south part of Scotland, is from E.N.E. to W.S.W.; and the same

is nearly true of those which compose the ridge of the Grampians on

the north, and the hills of Cumberland and Westmoreland toward the

south, though between the schistus of these three tracts, there is no

communication at the surface, each being entirely separated from the

one next it, by the interposition of secondary strata. I have already

mentioned the observations of Lord Webb Seymour and myself, at the

foot of Ingleborough; and it appears from them, that the vertical

schistus on which that mountain rests, though it still preserves an

eastern and western direction, varies several points from that of the

more northern strata. The strata of Wales return more to the first

mentioned direction, and those of Devonshire and Cornwall agree with

it very nearly. In all this, it will be easily conceived, that I do

not mean to speak with absolute precision, or to deny the existence of

great local irregularities. The result given is only a kind of average,

deduced from observations hardly susceptible of great exactness, and

not yet sufficiently multiplied to give to the conclusion all the

accuracy it may attain.

207. This tendency of the primary strata to take a uniform direction,

has also been observed in other countries. Saussure remarked in the

Alps, that the beds of schistus are generally parallel to the chains of

mountains composed of them;[104] and this remark is probably applicable

to all mountains consisting of primary strata. The general direction,

therefore, of the schistus of the Alps, must be confined between W.

10° S. and W. 40° S. In the Pyrenees, the direction of the strata is

about W.N.W.[105] If Saussure's rule may be depended on, the schistus

of the Altaic, and most of the other great chains in the old continent,

are in directions that run considerably to the south of west. The

Urals, and perhaps some other of the northern chains, are however

entirely different. In the Urals, as we learn not only from the general

direction of the chain, but from a section of it in the 10th volume of

the Nova Acta of Petersburgh (Tab. 12,) the direction of the strata is

nearly from N. to S. This last is probably the direction in the great

chains of South America; so that the uniformity of direction in the

primary strata, which some mineralogists would extend to those of the

whole earth, is certainly imaginary, though there can be no doubt that

it extends over very large portions of the earth's surface.[106]

[Footnote 104: Voyage aux Alpes, tom. i. § 577.]

[Footnote 105: Essai sur la Mineralogie des Pyrenées.]

[Footnote 106: It is perhaps unnecessary to observe, that the two

propositions, that the intersections of the strata with the horizon

are parallel lines; and that they are lines which reserve the same

bearing with respect to the points of the compass; are nearly the same

thing for tracts of moderate extent, but for large portions of the

earth's surface are extremely different. If, for instance, the belt

of primary vertical schistus, which traverses the south of Scotland,

were to be produced eastward in the same plane, from its northern

extremity, where its direction is E.N.E. and its latitude 55° 57', it

would cut the meridian always less obliquely as it advanced, till,

having increased it longitude about 26° 28', it would be at right

angles to the meridian, and its direction of consequence due east and

west. This would happen in the parallel of 58° 51', (on the shore of

the Gulf of Finland, near Revel,) the strata being now extended about

880 G. miles from the Siccar Point. Conversely, vertical strata, having

the same bearing with respect to the meridian, may be in planes very

much inclined to one another. A stratum which bears east and west in

Cornwall, and one that does the same at the east end of the Altaic,

will be in planes, which, if produced, would cut one another at right

angles. All this is sufficiently plain from the doctrine of the

sphere, and is mentioned here merely as a caution to prevent too hasty

conclusions from being drawn from any correspondence of bearing among

the strata of remote countries.

For the sake of those who would deduce the medium bearing of any body

of strata from a number of observations, it may be proper to take

notice, that the true average is not to be found by simply taking

an arithimetical mean among all the observations. A more exact way

is to work by the traverse table, as in keeping a ship's reckoning,

(supposing the distance run to be always unity,) and to compute from

the observed bearings the amount of all the southing or northing, and

also all the easting and westing. The sum of all the latter, divided

by the sum of all the former, is the tangent of the angle which the

general direction of the strata makes with the meridian.]

208. The tendency of the primary strata to remain straight in the

horizontal direction, and to be bent in the vertical, is a phenomenon

which points very directly to the causes from whence it has arisen. A

surface of simple curvature, or a surface straight in one direction,

is what the application of forces to different points of a plane,

which is flexible, though with a certain degree of rigidity, will

naturally produce. The supposition, therefore, that these strata were

once flat and horizontal, and were impelled upward from that situation

before they had become rigid or hard, will explain their having the

kind of curvature which removes them as little as possible from their

original condition. But no other hypothesis affords any reason why

they should have that curvature more than any other. From the falling

in of roofs of caverns, we might expect fracture and dislocation,

without any order or regularity; but certainly no bending or sinuosity,

nor any symmetrical arrangement. If, as some mineralogists allege,

the curvature, as well as inclination of the strata, arose from the

irregularities of the bottom on which they were deposited, why is the

former in one dimension only, and why is it not in every direction,

like that of hills and valleys, or the actual surface of the earth?

Or, lastly, if the whole structure of the primitive mountains is an

effect of crystallization, and if these mountains are now such as

they have ever been from the time of their consolidation, whence is

it, that, in their bendings the law just mentioned is so constantly

observed? Indeed, the idea of ascribing the inflections of the strata

to crystallization, though suggested by Saussure,[107] and since

become a favourite system with several mineralogists, appears to me

in the highest degree unsatisfactory and illusive. The purpose for

which crystallization is here introduced, is not to give a specific

figure to a particular substance, but to arrange the substances which

it has formed and figured, according to certain rules; a work which

we know not how it is to perform, and in which we have no experience

of its power. Accordingly, this principle does not account, in any

way whatever, for the circumstances which attend the inflection of

the strata, for the simple curvature which they affect, nor for that

parallelism of their layers, which, in all their bendings, is so

accurately preserved. It does, indeed, so little serve to explain

these facts, that, were the appearances completely reversed; did the

strata assume the most complex, instead of the most simple curvature;

instead of equidistant, were they converging, or alternately receding

and approaching to one another; the theory of crystallization might

be equally applied to them. The state of the phenomena is a matter of

perfect indifference to such a theory as this; all things are explained

by it with the same facility; the straight and the crooked, the square

and the round, the moveable and the immoveable. Is it not evident that

such an explanation is a mere word; or, if any thing more than a word,

an expression of our ignorance, so awkward and indirect, as to deprive

us of whatever credit might have been gained by a plain and candid

avowal of it?

[Footnote 107: Voyages aux Alpes, tom. i. § 475.]

It should never be forgotten, that a theory which accounts for _any

thing_, and a theory which accounts for _nothing_, stand precisely

on the same footing, and ought to be banished from all parts of

philosophy, as they have been from those sciences which are justly

honoured with the name of accurate. The animated orbs of Aristotle,

and the vortices of Des Cartes, have long ceased to be mentioned in

physical astronomy; the first, because, they accounted for every thing

alike; the second, because, when they accounted for one thing, they

never could be made to account for another. Both theories, therefore,

have very properly been rejected; and, when geology shall undergo a

similar purification, the principle we have been considering will not

be the only sacrifice required of the Neptunian system.

209. An appearance observed in some kinds of primary schistus, which

clearly indicates their deposition by water, and in planes very

different from those in which we now see them, though it might have

been introduced before, is also much connected with the present

argument. This appearance consists of small wavings or undulæ on the

surface of the plates of schistus, precisely similar to these marks

which are left by the sea on a gently inclining beach of sand, at the

ebbing of the tide. All the species of schistus do not seem to afford

instances of these wavings. The rocks which do so, are, I think,

chiefly of the argillaceous kind, but often highly indurated; so that

the laminæ containing the impressions are not to be torn asunder but

with great difficulty. Instances of it abound in the schistus of

Berwickshire, and are also not unfrequent in that of Galloway. All must

agree about the agent which produced these marks; it could be no other

than the sea; but it must have been the sea acting on loose, small and

round particles, lying on a surface which was nearly horizontal.

210. Dr Hutton's theory is no where stronger, than in what relates

to the elevation and inflection of the strata; points in which all

others are so egregiously defective. The phenomena to be connected

are here extremely various, and even in appearance contradictory:

the horizontally of one part of the strata; the inclined or vertical

position of another; the perfect planes in which one set are extended;

the breaking and dislocation found in a second; the inflection and

sinuosity of a third; and almost every where the utmost rigidity and

induration, combined with appearances of the greatest softness and

flexibility; the preservation of a parallelism of superficies in the

midst of so much irregularity, and the assumption of a determinate

species of curvature, under circumstances the most dissimilar; all

these appearances were to be connected with one another, and with

the consolidation of the strata, and this is done by the twofold

hypothesis, of aqueous deposition, and the action of subterraneous

heat. When these circumstances are fairly considered, and when the

shifts which other systems are put to on this occasion are remembered,

I think it will be granted, that few attempts at generalization have

been more successful, than that which has been made by the Huttonian

Theory.

211. To the fact of the elevation of the strata, the study of geology

is much indebted. The stratified form of a great proportion of the

earth's surface, gives to minerals that organization and regularity,

which makes their disposition an object of science, and their inclined

position serves to bring that organization into view, from far greater

depths than we can ever reach by artificial excavations. If, for

instance, the termination of strata, that make with the horizon an

angle of 30°, lying one over another, is seen for a horizontal distance

of two miles; then it is certain, that if these strata have that extent

under ground, which may be reasonably supposed, the thickness of the

whole mass, measured by a line perpendicular to its stratification, is

half the horizontal distance, or amounts to one mile. It would also

require a pit to be sunk from the uppermost of these strata, to the

depth of (2 miles × tan 30°, =) 6093 feet before it could intersect the

undermost; and therefore, if we suppose the same stratum to preserve

the same character for the extent of some miles, we obtain the same

information from inspecting the edge-seams, and see in reality as far

into the bowels of the earth, as if we had sunk a perpendicular shaft

to the depth of 6000 feet.

In general, the length of the horizontal line drawn across the strata,

from the lowest in position to the highest, multiplied into the sine of

the inclination of the strata to the horizon, gives the thickness of

the whole, measured perpendicularly to the plane of the stratification:

and the same horizontal distance, multiplied into the tangent of the

inclination, gives the actual depth at which the lowest stratum would

meet a perpendicular to the horizon, drawn from the highest extremity

of the upper stratum.

In many cases, the extent of stratified materials admitting of such

an examination as this, is much greater than has now been supposed.

M. Pallas describes a range of hills on the south-east side of the

peninsula of the Tauride, which is cut down perpendicularly toward the

sea, and offers a complete section of the parallel beds of a primary,

or, as he calls it, an ancient limestone, inclined at an angle of

45° to the horizon; and this section continues for the length of 130

_versts_, or about 86 English miles. The beds are so regular, that M.

Pallas compares them to the leaves of a book.[108] The height of these

hills does not exceed 1200 feet, but the real height of the uppermost

stratum above the undermost, is 86 × √1/2 = 86 × 5/7 = 61 miles nearly.

[Footnote 108: See Nova Acta Acad. Petropol. tom. x. (1792,) p. 257.]

If therefore we conceive that there is no shift in all this great

system of strata, we in reality are enabled, by means of it, to see no

less than 61 miles into the interior of the earth, nearly a 65th part

of the radius of the globe. It is true, that we can hardly suppose so

great a body of strata to have been raised without shifting, so that

we must diminish this depth considerably; but were it reduced even to

one-half it will appear, that men see much farther into the interior

of the globe than they are aware of, and that geologists are reproached

without reason for forming theories of the earth, when all that they

can do is but to make a few scratches on its surface. Art indeed can do

little more; but nature supplies the deficiency, and makes discoveries

to the attentive observer, on the same great scale with her other

operations.

The simplest account that can be given of the vast body of parallel and

highly inclined strata just mentioned, is, that it consists of the ends

of horizontal strata, or of strata not greatly inclined, that have been

forced up when they were all soft and flexible. This is a much more

conceivable supposition than Pallas's, viz. that the greater part of

this mass has sunk down into some vast cavern in the interior of the

earth.

NOTE XIII. § 53.

_Metallic Veins._

212. The large specimens of native iron found in Siberia and Peru,

mentioned above, § 51, are among the most curious facts in the natural

history of metals. It has been doubted, however, by some, whether they

really belong to natural history, or are not rather to be accounted

artificial productions. If they had been found in the heart of rocks,

or in the midst of metallic veins, no doubt of this sort could possibly

have been entertained; but, as they lie quite on the surface, in the

middle of flat countries, and at a distance from any known vein of

metal, the conjecture that they may be artificial, and the remains of

the iron founderies of ancient and unknown nations, is at first sight

not entirely destitute of probability. This probability, however, will

appear to be the less, the more carefully the specimens are examined.

The metal is too perfect, and the masses too large, to have been melted

in the furnaces, or to have been transported by the machinery, of a

rude people. The specimen in South America weighs 300 quintals, or

about 15 tons, and is soft and malleable.[109] The Siberian specimen,

described by Pallas, is also very large; it is soft and malleable, and

full of round cavities, containing a substance, which, on examination,

has been found to be chrysolite.[110] Now, it is certainly quite

impossible, that, in an artificial fusion, so much chrysolite could

have come by any means to be involved in the iron; but, if the

fusion was natural, and happened in a mineral vein, the iron and the

chrysolite were both in their native place, and their meeting together

has nothing in it that is inexplicable.

[Footnote 109: Phil. Trans. 1788, p. 37. also p. 183, &c.]

[Footnote 110: Kirwan's Mineralogy, vol. ii. art. Native Iron.]

213. Some circumstances in the description of the specimen in South

America, such as the impressions of the feet of men and of birds on its

surface, are not to be accounted for on any hypothesis, and certainly

require more careful investigation. It is said, that this iron is

very little subject to rust, and the analysis of a piece of it by

PROUST makes it probable, that it owes this quality to its union with

nickel.[111] It appears, also, that the country of Chaco, where this

specimen was found, affords many others of the same kind, one of which

is mentioned in the description above referred to. That country lies

on the east side of the Plata, and is a plain extremely level, and of

vast extent, without any appearance of mineral veins; but such veins

may nevertheless exist undiscovered, in a tract subject to periodical

inundations, and where the native rock is covered with alluvial earth

and gravel to a great depth. The veins maybe washed away, and the more

durable substances, such as those pieces of native iron, may be left

behind; and, though they must be of a formation extremely ancient,

according to this hypothesis, they may not have been very long on the

surface.

[Footnote 111: Annales de Chimie, tom. xxxv. Messidor, p. 47.]

214. Specimens of native iron have been found, less remarkable than

the preceding for their size, but in circumstances that excluded

all idea of artificial fusion. Of this sort was MARGRAAF'S specimen

of native iron, the first of the kind that was known; it consisted

of small bits of soft and malleable iron, found in the heart of a

brown iron-stone.[112] This makes it certain, that native iron is a

natural production, and the mere circumstance of great magnitude, in

the specimens before mentioned, does not entitle us to doubt of their

having that same origin. It is a circumstance, besides, not in the

least material to this argument; the smallest piece of native iron

being as much a proof of fusion as the greatest; and the specimen

of Margraaf being just as conclusive in favour of the Huttonian

Theory, as those of Pallas or De Celis, supposing their reality in

mineral productions to be completely established. À metal malleable

and ductile, in ever so small a quantity, cannot be the result of

precipitation from a menstruum, without a very particular combination

of circumstances. Such a metal, can the other hand, can be readily

produced by igneous fusion; so that here the negative and affirmative

parts of the inductive argument may both be regarded as complete.

[Footnote 112: Kirwan's Mineralogy, vol. ii. p. 156.]

215. Mr Kirwan, in order to account for the magnitude of the two large

specimens mentioned above, supposes, that small pieces of native iron

(about the formation of which he appears to have no difficulty) have

been originally agglutinated by petroleum, and left bare, when the

surrounding stony or earthy masses either withered or were washed

off.[113] This is no doubt the most singular of all the opinions which

have been advanced on the subject; and, as it borrows nothing from

analogy, it admits of no proof, and requires no refutation. None but a

chemist of eminence could have ventured with impunity on an assertion

so inconsistent with all the phenomena and principles of his science.

[Footnote 113: Geol. Essays, p. 405.]

216. A remark of the same author, on the subject of the native gold

found in the county of Wicklow in Ireland, is entitled to more

attention. "That these lumps of native gold," he says, "were never in

fusion, is evident from their low specific gravity, and the grains of

sand found in the midst of them. I found the specific gravity of a lump

of the size of a nutmeg to be only 12800, whereas, after fusion, it

became 18700."[114]

[Footnote 114: _Ibid._ p. 402.]

This argument is plausible; but, I think, nevertheless inconclusive.

The sand found in the gold, accounts, at least in part, for its

lightness. It is only by repeated fusions that any of the metals is

brought to its utmost purity and highest specific gravity; and on no

supposition can the melting of gold in the mineral regions, be very

likely to separate it from heterogeneous substances. That quartzy

sand should be found in it, after such a process, is naturally to be

expected. The impressions which the quartz crystals have left on the

Wicklow gold, would be received as a full proof of the fusion of that

metal, if geologists always regulated their theories by the principles

which determine the belief of ordinary men.

217. Don Rubin de Celis, in the paper referred to above, mentions some

masses of silver found at Quantajaia, and also some dust of platina, in

terms that excite a strong desire to have more information concerning

them. They are considered by him as effects of volcanic fire; so we

may conclude, that they contain evident marks of fusion, and would in

this system be ascribed to that heat, from which volcanic fire is but a

partial and accidental derivation.

218. The state also in which gold and silver are often found pervading

masses of quartz, and shooting across them in every direction,

furnishes a strong argument for the igneous origin, both of the metal

and the stone. From such specimens, it is evident, that the quartz

and the metal crystallized, or passed from a fluid to a solid state,

at the same time; and it is hardly less clear, that this fluidity did

not proceed from solution in any menstruum: For the menstruum, whether

water or the _chaotic fluid_, to enable it to dissolve the quartz,

must have had an alkaline impregnation; and, to enable it to dissolve

the metal, it must have had, at the same time, an acid impregnation.

But these two opposite qualities could not reside in the same subject;

the add and alkali would unite together, and, if equally powerful,

form a neutral salt, (like sea-salt,) incapable of acting either on

the metallic or the siliceous body. If the acid was most powerful, the

compound salt might act on the metal, but not at all upon the quartz;

and if the alkali was most powerful, the compound might act on the

quartz, but not at all on the metal. In no case, therefore, could it

act on both at the same time. Fire or heat, if sufficiently intense,

is not subject to this difficulty, as it could exercise its force with

equal effect on both bodies.

219. The simultaneous consolidation of the quartz and the metal is

indeed so highly improbable, that the Neptunists rather suppose, that

the ramifications in such specimens as are here alluded to, have been

produced by the metal defusing itself through _rifts_ already formed

in the stone.[115] But it may be answered, that between the channels

in which the metal pervades the quartz, and the ordinary cracks or

fissures in stones, there is no resemblance whatever: That a system of

hollow tubes, winding through a stone, (as the tubes in question, must

have been, according to this hypothesis, before they were filled by

the metal,) is itself far more inconceivable than the thing which it

is intended to explain; and lastly, that if the stone was perforated

by such tubes, it would still be infinite to one that they did not all

exactly join, or inosculate with one another.

[Footnote 115: Geol. Essays, p. 401.]

220. The compenetration, as it may be called, of two heterogeneous

substances, has here furnished a proof of their having been melted by

fire. The inclusion of one heterogeneous substance within another,

as happens among the spars and drusens, found so commonly in mineral

veins, often leads to a similar conclusion. Thus, from a specimen of

chalcedony, including in it a piece of calcareous spar, Dr Hutton

has derived a very ingenious and satisfactory proof, that these two

substances were perfectly soft at the same time, and mutually affected

each other at the moment of their concretion.[116]

[Footnote 116: Theory of the Earth, vol. i. p. 93.]

Each of these substances has its peculiar form, which, when left to

itself, it naturally assumes; the spar taking the form of rhombic

crystals, and the chalcedony affecting a mammalated structure, or a

superficies composed of spherical segments, contiguous to one another.

Now, in the specimen under consideration, the spar is included in the

chalcedony, and the peculiar figure of each is impressed on the other;

the angles and planes of the spar are indented into the chalcedony,

and the spherical segments of the chalcedony are imprinted on the

planes of the spar. These appearances are consistent with no notion of

consolidation that does not involve in it the simultaneous concretion

of the whole mass; and such concretion cannot arise from precipitation

from a solvent, but only from the congelation of a melted body. This

argument, it must be remarked, is not grounded on a solitary specimen,

(though if it were it might still be perfectly conclusive,) but on a

phenomenon of which there are innumerable instances.

221. According to this theory, veins were filled by the injection of

fluid matter from below; and this account of them, which agrees so

well with the phenomena already described, is confirmed by this, that

nothing of the substances which fill the veins is to be found any where

at the surface. It is not with the veins as with the strata, where, in

the loose sand on the shore, and in the shells and corals accumulated

at the bottom of the sea, we perceive the same materials of which these

strata are composed. The same does not equally hold of metallic veins:

"Look," says Dr Huston, "into the sources of our mineral treasures? Ask

the miner from whence has come the metal in his veins? Not from the

earth or air above, not from the strata which the vein traverses: these

do not contain an atom of the minerals now considered. There is but

one place from whence these minerals may have come; this is the bowels

of the earth; the place of power and expansion; the place from whence

has proceeded that intense heat, by which loose materials have been

consolidated into rocks, as well as that enormous force, by which the

regular strata have been broken and displaced."[117]

[Footnote 117: Theory of the Earth, vol. i. p. 130.]

222. The above is a very just and natural reflection; but if, instead

of interrogating the miner; we consult the Neptunist, we will receive

a very different reply. As this philosopher never embarrasses himself

about preserving a uniformity in the course of nature, he will tell

us, that though it may be true, that neither the air, the upper part

of the earth's surface, nor even the sea, contain at present any thing

like the materials of the veins, yet the time was when these materials

were all mingled together in the chaotic mass, and constituted one

vast fluid, encompassing the earth; from which fluid it was, that the

minerals were precipitated and deposited in the clefts and fissures of

the strata.

223. It is alleged, in proof of this hypothesis, that mineral veins are

found to be less rich as they go farther down, whereas they ought to

be richer if they were filled by the projection of melted matter from

below. But the fact, that mines are less rich as they descend farther,

though it may hold in some instances, is not general, and may therefore

be supposed to arise from local causes, such as are, in respect of us,

accidental, and beyond the limits to which our theories can be expected

to reach. Thus the mines of Mexico and Peru are said to be subject

to the preceding rule; but in the mines of Derbyshire and Cornwall,

the very contrary is understood to take place. Besides, what we are

pleased to call the riches of a mine, are riches relatively to us, and

relatively to a distinction which nature does not recognise. The spars

and veinstones which are thrown out in the rubbish of our mines, may be

as precious in the eyes of nature, as conducive to the great objects

of her economy, and are certainly as characteristic of mineral veins,

as the ores of silver or gold, to which we attach so great a value.

Unless the former are in smaller quantity, or less highly crystallized

at great than at small depths, which I believe is not alleged, no

conclusion can be drawn from substances, which occupy in general but a

small proportion of any vein, and, in their dissemination through it,

do not seem to be always guided by the same law.

224. Again, if the veins were filled by deposition from above, we ought

to discover in them such horizontal stratification as is the effect of

deposition from water, and we should perceive no marks of the materials

having been introduced with violence into their place. The Neptunists

cannot object to the trial of their theory by these two frets.

As to the first, it is acknowledged, that there is a certain regular

disposition of the substances in mineral veins, as stated § 59, but it

is one which has hardly any thing in common with the real phenomena

of stratification. It consists in the distribution of the principal

substances in coats parallel to the sides of the vein, each substance

forming a separate coat. In a vein, for instance, containing quartz,

fluor, calcareous spar, lead, &c. we might expect to find a lining of

quartz crystals, applied immediately to the walls of the mine, and

following exactly the irregularities of their surface; next, perhaps,

a coat of fluor, then of calcareous spar, and last of lead ore in the

centre of the vein, the same order being observed on the opposite

side. These successive coats, it is material to remark, are not in

planes, but in uneven surfaces, of which the inequalities are evidently

determined by those of the walls, that is, of the rock which forms

the sides of the vein; neither are they horizontal, but are parallel

to the walls, whether these be perpendicular or inclined. Here,

therefore, there is no appearance of the action of that statical law

which has directed the arrangement of the other strata, and which tends

to make the plane of every stratum deposited by water perpendicular

to the direction of gravity. The coating of the veins has therefore

been performed under the conduct of some other power than that which

presides over aqueous deposition. If, as the Neptunists maintain, the

materials in the veins were deposited by water, in the most perfect

tranquillity, it is wonderful that we do not find those materials

disposed in horizontal layers, across the vein, instead of being

parallel to its sides; and it seems very unaccountable, that the common

strata, deposited as we are told while the water was in a state of

great agitation, have so rigorously obeyed the laws of hydrostatics, (§

38.) and acquired a parallelism in the planes of their stratification,

which approaches so often to geometrical precision; while the materials

of the veins, in circumstances so much more favourable for doing the

same, have done nearly the reverse, and taken a position, often at

right angles to that which hydrostatical principles require. This is a

paradox which the Neptunian system has created, and which therefore it

is not very likely to resolve.

225. Mere words should have little power to mislead, in a science which

treats of sensible objects, such as are always easily subjected to the

examination of sight or of touch; yet there is some appearance as if

the Neptunists were misled in this, and other instances, by the term

_stratification_. Though an incrustation on the perpendicular face of a

rock has very little affinity to a stratum, such as we are accustomed

to see deposited by water, yet the same name being once imposed on

both, mineralogists have proceeded to reason concerning them, as if

they were precisely the same thing, and were both to be ascribed to

the same cause. Indeed every perpendicular or highly inclined bed of

stone, is inexplicable as an effect of aqueous deposition, in a system,

unprovided, as the Neptunian is,[118] with the means of raising up

such beds from a horizontal into a vertical position. This observation

may also be extended to all cases of vertical stratification. Water

cannot directly arrange its deposits in planes highly inclined, and

therefore I have often wondered to see the Neptunists contending so

eagerly for the stratification of certain rocks, such as granite,

which, being vertical, or highly inclined, was much less friendly to

their system than the entire absence of all stratification would have

been. I was disposed to admire their candour, when the use which

they made of the fact convinced me, that I ought only to wonder at

their inconsequential reasoning. The Huttonian Theory is, indeed, the

only one which possesses the means of reconciling the elevation of

the strata with their horizontal deposition, and which is entitled to

consider stratification, in whatever plane it may be, as originally the

work of the ocean. The geologists who attach themselves exclusively to

the action of water, will never be able to extend the dominion of that

element so far as Dr Hutton has done, by combining it with fire.

[Footnote 118: See preceding note.]

226. But, though the Neptunian system were provided with engines,

powerful enough to raise up strata from a level to a vertical plane,

this would avail nothing in the present instance; since, on no

supposition, can the incrustations on the perpendicular sides of a

vein have ever been horizontal. On no supposition, therefore, can

these incrustations be received as a proof of aqueous deposition: it

may indeed be certainly inferred from them, that the matter which they

consist of was fluid at the time of their formation; but the absence of

all appearance of a horizontal disposition, in any part of the vein,

amounts nearly to a demonstration, that this fluidity did not proceed

from solution in a menstruum. We must therefore conceive the coats

to have been formed during the refrigeration of the melted matter

injected from the mineral regions into the clefts and fissures of the

strata. (§ 59.)

227. Mineral veins, particularly at their intersections with one

another, contain abundant marks of the most violent and repeated

disturbance (§ 56.). Not to mention that they owe their first formation

to the fracture and displacing of rocks already consolidated, it

appears, that they have originated at very different periods, and that

the birth of each has been accompanied with convulsions, which shook

the foundations of the earth. In Cornwall, for instance, the principal

veins, and those which they distinguish particularly by the name of

_Lodes_, have nearly the same direction with the strata or vertical

schistus, extending from about E. N. E. to W. S. W. These, however,

are often intersected nearly at right angles by other mineral veins,

called _Cross Courses_, and this hardly ever happens without the latter

moving, or, as it is called, heaving the former out of their direction.

This plainly indicates, that the cross courses are of later origin

than the others, and that their formation was accompanied with such a

force, as must, in many substances, have moved the whole body of rock

which constitutes the promontory of Cornwall, and probably much more,

for several yards, in a horizontal direction. Sometimes, also, both

the longitudinal and the cross vein are forced out of their place by

a third. These disturbances arise not only from mineral veins, but

from veins of porphyry and granite, the production of which has been

attended with no less violence than of the others.

228. What is here said of Cornwall, is the history, in some degree,

of all mineral countries whatever. The great horizontal _translation_

which has thus accompanied the formation of veins; the movement

impressed on such vast bodies of rock, and the frequent renewal of

these immense convulsions; are not to be explained by the mild and

tranquil dominion of the watery element. They require the utmost power

that is known any where to exist, and were it not for the admonitions

of the volcano and the earthquake, we might doubt if even subterraneous

heat itself possessed an energy adequate to these astonishing effects.

229. From the _heaving_ of one vein by another, it is evident, that

there was a force of protrusion in the direction of one of them, that

acted at the time of its formation. This force cannot be accounted

for on the supposition that veins were produced by the mere shrinking

of the strata; for the rocks could not, in that case, have been rent

asunder, and impelled forward at the same time. It appears most likely,

that fissures in the strata were made, at least in many instances,

and the matter poured into them, nearly at the same time, both being

effects of the same cause, the expansive force of subterraneous heat.

230. It is remarked, at § 56, that the shifting of the strata is best

observed where the veins make a transverse section of beds of rock,

considerably inclined to the horizon. It is also true, that in some

cases the near approach of the strata to the level, may make the shifts

produced by the veins very easy to be discovered. Thus in Derbyshire,

where the mineral veins are in secondary strata, nearly horizontal,

there is almost no instance in which the corresponding strata are not

observed to be on different levels, on the opposite sides of the same

vein.

231. The fact described by De Luc, and referred to at § 55, may, for

what we know of it, admit of being explained in two ways. The great

wedge of rock which appears to be insulated between two branches of the

same vein, may either be a mass that has been broken off, and sustained

by the melted matter that flowed all around it; or, it may be a mass

of rock contained between two veins that are in reality distinct, and

of different formation. Whether this last supposition is the truth,

would probably be evident from a careful examination of both parts

of the vein; as some difference of character cannot fail to be the

consequence of different formation. If no such difference is observed,

the two branches must be supposed to belong to the same vein, and the

only probable explanation of the insulation of so large a mass of rock

will be by the first mentioned supposition. This fact, therefore,

notwithstanding the great attention M. De Luc has bestowed on it,

still requires further examination, before it can be decided whether

it inclines to the Huttonian Theory, as on the first supposition, or

is, as on the latter hypothesis, equally balanced between it and the

_Wernerian_.

232. Whatever be the case with this fact, the general one of pieces of

rock being found insulated in veins, is certainly favourable to the

notion of an injected and ponderous fluid having originally sustained

them. Where, as happens in some instances, the stones contained in

the veins have no affinity to any of the rocks above, they cannot

be supposed to have come any how but from below, and to have been

carried up by the matter of the vein. The instance from the slip at the

Huddersfield Canal has been already mentioned.

233. The preceding observations have been principally directed against

that theory of veins which supposes them to have been filled by

deposition from water. There is another theory maintained by some

of the Neptunists, that the metals in veins were introduced there by

infiltration.[119] This opinion is sufficiently refuted by the fact,

that rarely any metallic ore is found out of the vein, or in the rock

on either side of it, and least of all where the vein is richest.

This is inconsistent with the notion of the ore being carried into

the vein by water percolating through the adjacent rocks, unless some

satisfactory reason is assigned, which determined the water to leave

the ore in the vein and no where else. Besides, this hypothesis does

not account for the formation of the spars and veinstones which fill

the vein, and which appear clearly to have been brought there at the

same time with the ore, and no doubt by the same cause.

[Footnote 119: Geol. Essays, p. 401.]

234. The veins, properly so called, are indefinitely extended; but

there are also thin plates of spar, and of crystals of different kinds,

often found included in rocks, and shut in on all sides, to which the

name of veins is commonly applied. These last ought certainly to be

distinguished from the former, and may not improperly be called _Plate

Veins_ or _Lenticular Veins_, the plate or cake of spar of which they

consist having very often the form of a lens, though, as may be

supposed, considerably irregular. Either of these terms being derived

entirely from external characters, has the advantage of involving

nothing theoretical.

The lenticular veins are certainly not formed like the usual mineral

veins, by injection, since they are shut in, on all sides, by the solid

rock. When they are found, therefore, in stratified rocks, such as

have not themselves been melted, we must conceive them to be composed

of materials more fusible than the surrounding rock, so that they

have been brought into fusion by a degree of heat which the rest of

the rock was able to resist, and, on cooling, have assumed a sparry

structure. When they are found in rocks, of which the whole has been

fluid, they must be considered as component parts of that mass, which,

by an elective attraction, have united with one another, and separated

themselves from the substances to which they had less affinity.

The veins of this kind seem to be connected with those called in

Derbyshire _Pipe Veins_, in which the ores of metals are sometimes

found. The pipe veins, indeed, are not in all cases completely

insulated, but sometimes communicate with the veins properly called

mineral. I am too little acquainted, however, with their natural

history, to Be able to say with certainty to which of the two species

they ought to be referred.

NOTE XIV. § 75.

_On Whinstone._

235. To the facts and reasonings given above, I shall, in this note,

add a few remarks, tending to show, that whinstone is not of volcanic,

nor of aqueous, but certainly of igneous origin.

It is asserted, (§ 62,) that carbonate of lime and zeolite are often

contained in whinstone, but never in lava, and that this circumstance

may sometimes serve to distinguish these stones from one another. With

respect to carbonate of lime, in particular, it seems evident, that

this substance cannot enter into the original composition of any lava,

because the same heat which melted the lava, would, where there was no

greater pressure than the weight of the atmosphere, expel the carbonic

acid and produce quicklime. Notwithstanding this, rocks containing

carbonate of lime, have often been considered as lavas, into the pores

and cavities of which, calcareous matter having been carried by the

infiltration of water, had crystallized into spar. Thus SPALLANZANI,

in his account of the Euganean Hills, in Lombardy, describes some of

the rocks as abounding at their surface, and even in their interior,

with air-bubbles of various sizes, from such as are hardly perceptible,

to some that are half an inch in diameter; and which, he says, are all

of an oval figure, with their longest diameters in the same direction.

This he considers as a proof that the rock is a genuine lava; for the

air-bubbles prove the stone to have had its fluidity from fire; and

by their elongation in the same direction they prove, that the mass

when fluid was also in motion. Spallanzani adds, that _many of these

cavities are filled with crystals of the carbonate of lime, an effect

of the infiltration of water_.[120]

[Footnote 120: Voyages dans les deux Siciles, tom. iii. p. 157. Edit.

de Faujas de St Fond.]

236. Though the argument here advanced for the igneous origin of the

rock may be admitted as conclusive, the introduction of calcareous

spar into it by infiltration must still be questioned. Lava, except

in a state of decay or decomposition, is not readily penetrated by

water; and, if it were, the filling of cavities with spar, by means

of the water percolating through them, would still be subject to many

difficulties, (§12.). Besides, whinstone rocks are frequently found so

full of calcareous spar, or of zeolite, that they would become porous

to such a degree, if the cavities filled with these latter substances

were all empty, that they could hardly sustain their own weight, and

much less that of the great masses of rock incumbent on them. In such

cases, it is certain, that the crystallized substances were part of the

original composition of the rock. The truth is, that the infiltration

of the water is a mere gratuitous assumption, introduced for the

purpose of explaining the existence of carbonated lime in a stone which

had endured the action of intense heat: and this assumption ought of

course to be rejected, if the phenomenon can be explained by a theory,

that is in other respects conformable to nature. The spar, then, may be

considered as a proof, that the rocks in question are to be numbered

with those unerupted lavas which have flowed deep in the bowels of the

earth, and under a great compressing force. This is the more probable,

that the Euganean Hills, like some whinstone hills in our own country,

have, in certain places, a covering of slaty and calcareous strata

incumbent on them, even at their summits,[121] so that the torrent of

melted stone, of which they are admitted to consist, cannot have flowed

from the mouth of a volcano. I do not mean to say, that there are

among these hills no vestiges of volcanic explosion. I am very far from

having _data_ sufficient for drawing this conclusion; but I believe it

may be safely affirmed, that the bulk of them is no more composed of

volcanic lava, than the basaltes of Staffa, or of the Giant's Causeway.

[Footnote 121: Phil. Trans. 1775, p. 34.]

237. But, besides the evidence deduced from calcareous spar and

zeolite, against the rocks containing them being real lava, there are

other marks, even less equivocal perhaps, that distinguish the lavas

which we suppose to have flowed in the mineral regions, from those

which have actually flowed on the surface. These are what we collect

from the disposition, the organization, or, as we may say, the physical

geography of whinstone countries, unlike, in so many respects, to that

of volcanic countries. The shape of whinstone hills; their large flat

terraces, rising one above another; their perpendicular faces, and the

correspondence of their heights even at considerable distances; have

nothing similar to them in the irregular torrents of volcanic lavas.

The phenomena of the former are also on a scale of magnitude very far

exceeding the latter, and clearly indicate, that though both have been

produced by fire, it has been by fire in very different circumstances,

and regulated by very different laws. The structure of the two kinds

of rock agrees, in many respects, and so does their chemical analysis;

but their disposition and arrangement are so dissimilar, that they

cannot be supposed to be of the same formation.

238. This argument, I believe, was first stated by Mr Strange, in

a letter to Sir JOHN PRINGLE, published in the 65th volume of the

_Philosophical Transactions_.[122] That intelligent observer, after

visiting the countries in Europe most remarkable either for burning,

or for what are accounted, extinguished volcanoes, and examining them

with a very discriminating eye, remained convinced, that there are two

distinct species of rock, which both owe their origin to fire; but

to fire acting in circumstances and situations extremely different.

The first is the common volcanic lava; the other, to which he gives

the name of a basaltine rock, comprehends such rocks as the Giant's

Causeway, the basaltes of the Vivarais, of the Euganean Hills, &c.

and differs in nothing from that which is called here by the name

of whinstone. Mr Strange conceived, that the one of these kinds of

stone could, no more than the other, be accounted the work of aqueous

deposition, but was led to the distinction just mentioned, by observing

the organization and arrangement in the rocks of the latter kind, and

comparing them with the disorder and ruin that every where mark the

footsteps of volcanic fire He does not pretend to determine the nature

of the fire to which the basaltine rocks owe their formation, nor the

circumstances in which it has acted: he is satisfied with the negative

conclusion, that it is not volcanic; and his paper affords a specimen

of what is perhaps rare in any of the sciences, and certainly most rare

of all in geology, viz. a philosophic induction carried just as far as

the facts will bear it out, and not a single step beyond that point.

[Footnote 122: Account of Two Giants' Causeways in the Venetian State,

&c. by John Strange, Esq. Phil. Trans. vol. lxv. (1775,) p. 5, &c.]

239. Several other hints contained in this paper are highly deserving

of notice; for we not only find in it the notion of a formation of

basaltic rocks, igneous though not volcanic, but also that of their

simultaneous crystallization,[123] together with the suggestion, that

granite and basalt are of the same origin,[124] These opinions had not,

I believe, occurred at that time to any mineralogist except Dr Hutton,

nor had they been communicated by him to any but a few of his most

intimate friends; so that Mr Strange has without doubt all the merit

of a first discoverer. Indeed, without the knowledge of the principle

of compression, such as it is laid down by Dr Hutton, it was hardly

possible for him to proceed further than he has done. He remarked

the unburnt limestone that lies on the tops of some of the Euganean

basaltes, and seems to have been aware of the great difficulty, which

it was reserved for the Huttonian Theory to overcome. His letter

contains also some excellent general remarks on the rocks of the

Vivarais and Velay, which he had visited, before FAUJAS DE ST FOND had

published his curious and elaborate description of these countries.

[Footnote 123: Phil. Trans, _ubi supra_, p. 17.]

[Footnote 124: _Ibid._ p. 36 and 37.]

240. The cause of the peculiar structure which has just been observed

to distinguish whinstone from volcanic countries, is easily assigned

in the Huttonian Theory. According to that theory, the whinstone rocks

were formed, in the bowels of the earth, of melted matter poured into

the rents and openings of the strata. They were cast, therefore,

in those openings, as in a mould; and received the impression and

character of the rocks by which they were surrounded. Hence the tabular

masses of whinstone, which when soft have been interposed between

strata, and compressed by their weight, so as almost to have themselves

acquired the appearance of stratification. Hence the perpendicular

faces of the same rocks, produced by their being abutted when yet

soft, against the abrupt sides of the strata. The rocks which formed

those moulds have, in many cases, entirely disappeared; in others, a

part still remains, surrounding, or even covering, the basaltes, as in

the Euganean Hills, in those of the Val di Noto in Sicily, the rocks

near Lisbon,[125] and in different parts of Great Britain.

[Footnote 125: Recherches sur les Volcans Eteints du Vivarais; Lettre

du Dolomieu, p. 443.]

Above all, the veins of whinstone which intersect the strata, are the

completest proofs of the theory here given of these rocks, and the most

inconsistent, in all respects, with the hypothesis of their volcanic

origin.