Transcriber Note
Since § 134 appeared on page 143 and again on page 147, the Section
number on pages 147 and all succeeding were incremented. The Table of
Contents was also incremented respectively. Text emphasis denoted by
_Italics_. List of ERRATA below has been applied to the text.
ERRATA.
Page 44. line 4. from the bottom, _for_ that _read_ as
" 189. " 6. " _for_ appearenes _read_ appearances
" 464. " 4. " _for_ D'AUBENTON _read_ DAUBENTON
" 482. " 12. " _for_ adversaries _read_ adversary
ILLUSTRATIONS
OF THE
HUTTONIAN THEORY
OF THE EARTH
BY JOHN PLAYFAIR
F. R. S. EDIN. AND PROFESSOR OF MATHEMATICS
IN THE UNIVERSITY OF EDINBURGH.
=========================================================
Nunc naturalem causam quærimus et assiduam,
non raram et foriuitam.
SENECA.
=========================================================
EDINBURGH:
PRINTED FOR CADELL AND DAVIES, LONDON, AND
WILLIAM CREECH, EDINBURGH.
======
1802.
Entered in Stationers Hall.
NEILL & CO. }
Printers, Edinburgh }
ADVERTISEMENT.
THE Treatise here offered to the Public, was drawn up with a view of
explaining Dr Hutton's Theory of the Earth in a manner more popular and
perspicuous than is done in his own writings. The obscurity of these
has been often complained of; and thence, no doubt, it has arisen,
that so little attention has been paid to the ingenious and original
speculations which they contain.
THE simplest way of accomplishing the object proposed, seemed to be, to
present a General Outline of the System, in one continued Discourse;
and to introduce afterwards, in the form of Notes, what farther
elucidation any particular subject was thought to demand. Through the
whole, I have aimed at little more than a clear exposition of facts,
and a plain deduction of the conclusions grounded on them; nor shall
I claim any merit to myself, if, in the order which I have found it
necessary to adopt, some arguments may have taken a new form, and some
additions may have been made to a system naturally rich in the number
and variety of its illustrations.
OF the qualifications which this undertaking requires, there is one
that I may safely suppose my self to possess. Having been instructed by
Di Hutton himself in his theory of the earth; having lived in intimate
friendship with that excellent man for several years, and almost in the
daily habit of discussing the questions here treated of; I have had the
best opportunity of understanding his views, and becoming acquainted
with his peculiarities, whether of expression or of thought. In the
other qualifications necessary for the illustration o a system so
extensive and various, I am abundantly sensible of my deficiency, and
shall therefore with great deference, and considerable anxiety wait
that decision from which there is no appeal.
EDINBURGH COLLEGE, }
1st March 1802. }
TABLE
OF
CONTENTS.
INTRODUCTION. Object of a Theory of the Earth. Division of minerals
into _Stratified_ and _Unstratified_.
Page 1
SECTION I.
PHENOMENA PECULIAR TO STRATIFIED BODIES.
1. Materials of the Strata.
Page 4
Present strata composed of the remains of more ancient rocks, § 1.
Proofs from calcareous strata, § 2.--from siliceous, § 3.--from
argillaceous, § 4.--from bituminous, § 5, 6. Absence of organized
remains from the strata called _primitive_, not universally true,
§ 8, 9.--Term Primary substituted for Primitive. Composition from
the materials of more ancient rocks, § 10.
2. Consolidation of the Strata.
p. 15
Consolidation, what, § 11. Objections to aqueous consolidation, §
12, 13, 14. Compression affects the action of fire on bodies, §
15, 16, 17.--Igneous consolidation of minerals prove from fossil
wood, § 19.--From the flints in chalk, § 20.--from sandstone,
§ 21.--from the calcareous strata, § 23, 24, 25.--from the
argillaceous, § 26, 27.--from the bituminous, § 28, 29.--from the
saline, § 32. Salt mines in Cheshire. Trona of Africa, § 54, 35.
3. Position of the Strata.
p. 40
Strata formed at the bottom of the sea, § 36. Apparent elevation
not produced by the retreat of the sea, § 37.--Strata,
horizontal, when formed, § 38, 39. Disturbance of the strata
proved from their inclined position § 40, 41, 42.--from shifts,
&c. § 42. Shifts of different dates, _ib._ Disturbance of the
primitive strata visible at their junction with the secondary, §
43, 44. This disturbance produced by a force directed upward, §
45, 46. This force the effect of subterraneous heat, § 47, 48.
SECTION II.
PHENOMENA PECULIAR TO UNSTRATIFIED BODIES.
1. Metallic Veins.
p. 57
Veins defined. They contain substances that were once in fusion, §
49, 50. Metallic veins, native metals, &c. § 51. Native copper, §
52. Manganese, § 53. Fragments of rocks included in veins, § 55.
Shifting and heaving of veins, § 56, 57. Veins of different dates,
§ 58. Stratification not found in veins. Coating of the sides,
what, § 59. Metallic veins most common in primitive strata; but
not confined to them, § 60.
2. Whinstone.
p. 66
Enumeration of stones of this genus, § 61. Whin, whether in veins
or in masses, resembles lava, § 62. Is a subterraneous lava,
§ 63. Columnar structure an argument for fusion, § 64. Not
produced by drying, § 65. Whinstone penetrated by pyrites, § 66.
Induration of the strata in contact with whin, § 67 Coal charred
by whinstone veins, § 68. Disturbance of the strata by whinstone
veins, § 69. Phenomena of whin interposed between strata, § 70,
71. Transition from whin to strata not gradual. § 72. Agates and
chalcedonies in whinstone, § 74. This stone melted and reproduced
from fusion by Sir James Hall, § 75. Mineral alkali found in it
by Dr Kennedy, _ib._ Whinstones of different formation, § 76.
Porphyry a species or variety of whinstone, §77.
3. Granite.
p. 82
Granite defined. Exists in masses and veins, § 77. The basis
of other rocks, § 78. Its original fluidity inferred from
the crystallization of its parts, § 79. Its fusion, from the
structure of the Portsoy granite, § 80, 81.--from granite veins,
§ 82. General conclusion as to the igneous origin of minerals, §
83, 84, 85. Actual existence of subterraneous heat known from hot
springs, volcanoes, earthquakes, § 86. Volcanic fire seated deep
under the surface, § 87. Subterraneous heat not accompanied by
burning, § 88, 89. Transmission of subterraneous heat, so as to
produce hot springs, &c. § 90, 91.
SECTION III
PHENOMENA COMMON TO STRATIFIED
AND UNSTRATIFIED BODIES.
p. 97
Chemical agents which produce the decomposition of mineral
substances at the surface, § 92, 93. Mechanical agents, § 95, 96.
Proofs of wearing from the sea shore, § 97, 98. Rivers, § 99,
100. Defiles among mountains, § 102. Supply of the soil from the
decomposition of rocks, § 103. Gravel in the soil, § 104, 105.
Gold found in the soil, § 106. Tin, § 107. Proofs of waste from
mountainous countries, § 108, 109. Structure of Valleys, § 111.
Transportation of stones, § 112. Nearest measure of the waste,
§ 113. General remarks, § 114, 115. No production of minerals
on the surface, § 116. Reproduction at the bottom of the sea, §
117. Continued system of decay and renovation, § 118. Defence
against the charge of impiety, 119. Antiquity and order of the
revolutions of the globe, § 120, 121, 122, 123, 124. Consistency
with the Sacred Writings, § 125. Scope of this theory of the
earth distinguishes it from others; beauty and extent of its
views, § 126. New facts, § 127. Comparison of this theory with
that of Buffon, § 129. Of Lazzaro Moro, § 130. _Plutonic_ system,
§ 131. Distinguished by the principle of compression, § 132.
Explains the oblate figure of the earth, _ib._ Prejudices against
this system, § 133. What may be expected from the progress of
science, § 134.
NOTES AND ADDITIONS.
NOTE I.--Origin of Calcareous Earth.
p. 143
Dr Hutton's opinion on this subject accurately stated, § 135.
Misrepresented by Kirwan, § 136.
NOTE II.--Origin of Coal.
p. 147
Vegetable origin of coal. Opinion of Buffon, § 137.--of Arduino,
_ib._--of Lehman, § 138. Distinction attempted between wood coal
and mineral coal, § 139. Not of different origin, but gradually
pass one into the other, § 140. Bovey coal, § 141. Kirwan derives
the matter of mineral coal from the decomposition of hornblende,
&c. 143. Absurdity of this supposition, § 144, 145, 146, 147.
NOTE III.--Primitive Mountains.
p. 160
Lehman introduced the term Primitive mountains, § 149. Supposed
more ancient than organized bodies, § 150. Stratification of
primitive mountains denied by Pini, and maintained by Saussure, §
151.
NOTE IV.--Primary Strata not Primitive.
p. 163
Shells found in primary strata, § 152. Sandstone in primary
mountains, § 153. Quartzy sand in the schistus of the Grampians,
_ib._ Rocks distinguished by Werner into three orders, § 154.
Objections to this arrangement, § 155.
NOTE V.--Transportation of the Materials
of the Strata.
p. 171
The transportation of materials, objected to by the Neptunists, is
implied in their own system, § 156, 157, 158. Proofs of great
transportation from the animal and vegetable remains, found in
rocks, § 160.
NOTE VI.--Kirwan's Notion of Precipitation.
p. 180
Difficulty, of precipitating the materials dissolved in the chaotic
fluid, § 162. Insufficiency of the explanation attempted, _ib._
NOTE VII.--Compression in the Mineral Regions.
p. 181
Effects ascribed to compression by Newton, compared will the
effects ascribed to it in this theory, § 163. Fallacy of Kirwan's
argument concerning the fusion of Carrara marble, § 165, 166.
Heat of the mineral region may be supported without fuel, § 167.
Quotation from Newton's Optics, _ib._ General remarks, § 169.
NOTE VIII.--Sparry Structure of Calcareous
Petrifactions.
p. 190
Sparry and organic structure co-exist in certain fossils, § 171.
Sparry and stratified structure co-exist in gneiss, marble, &c. §
172.
NOTE IX.--Petroleum, &c.
p. 194
Petroleum, &c. from the distillation of coal, § 173. Gradation from
petroleum to coal often met with, § 174. Connection of amber and
coal, § 175. Why mines of blind coal have not always petroleum
mines near them, § 176.
NOTE X.--The Height above the Level of the Sea,
at which Marks of
Aqueous Deposition are now found.
p. 199
These marks consist either in stratification or in marine objects,
§ 177. The marks of stratification observed, 14739 feet above
the sea, § 178. Shells in Peru, 14190, § 179. Kirwan's mistake
concerning these shells, § 180. His error similar to VOLTAIRE'S,
§ 181.
NOTE XI.--Fracture and Dislocation
of the Strata.
p. 204
Slips, § 182. Rib of limestone in a slip near Huddersfield, § 183,
184. Singular fracture of pudding-stones at Oban in Argyleshire,
§ 185. Similar phenomena observed by Saussure between Nice and
Genoa, _ib._ Remarks on it, § 186.
NOTE XII.--Elevation and Inflection
of the Strata.
p. 209
Junction of primary and secondary strata, § 187. Breccia
incumbent on the primary, § 188. Junction of the primary and
secondary strata: At Torbay in Devonshire, § 190,--coast of
Berwickshire, § 191,--Cullen in Banffshire, § 193,--Ardencaple
in Dunbartonshire, Arran, &c. § 194,--Pembrokeshire,
§ 195,--Jedburgh, § 196,--Ingleborough in Yorkshire, §
197,--Cumberland, § 198. Inflection of the strata, § 199.
Remarkable instances in the Alps and Pyrenees, § 200, 201,--on
Ben-Lawers in Perthshire, § 202,--coast of Berwickshire,
_ib._--Plymouth, § 203. Strata suffering such inflections
have been soft and ductile, § 204. General property of these
inflections, § 205, 206. uniform stretch of the primary strata,
§ 207. Inferences as to the nature of the elevating force, §
208. Imperfection of other theories. Crystallisation, _ib._
Marks of undulæ in the schistus, § 209. Elevation of the strata
a stronghold of the Huttonian theory, § 210. Elevation of the
strata enables us to see far into the interior of the earth, §
211.
NOTE XIII.--Metallic Veins.
p. 239
Specimens of native iron, § 212, 213. Margraaf's specimen, § 214.
Kirwan's hypothesis, § 215. Increase of the specific gravity of
native gold by fusion, no argument against its igneous origin,
§ 216. Specimens of gold and silver shooting through quartz, an
argument in favour of the Huttonian theory, § 218, 219. Proof in
favour of the same from chalcedony including calcareous spar,
§ 220. Matter that fills veins not from above or from either
side, § 221. Opinion of the Neptunists, § 222. Supposed fact
that veins are less rich as the depth increases, § 223. No marks
of horizontal deposition in veins; their coating differs from
stratification, § 224. Neptunists appear to be misled by the term
Stratification, § 225, 226. Veins heave or shift one another,
§ 227. Vast force employed for that purpose, § 228. Veins of
different formation, § 231. Pieces of rock insulated in veins, §
232. Supposition that veins have been filled by infiltrations,
absurd, 233. _Lenticular_ veins, and Pipe veins, § 234.
NOTE XIV.--On Whinstone.
p. 260
Whinstone, neither of volcanic nor aqueous formation, § 235.
Zeolite and carbonate of lime included in whinstone, but not in
lava, _ib._ Not introduced by infiltration, § 236. Disposition
of whinstone mountains differs from that of streams of lava,
§ 237. This argument first employed by Mr Strange, § 238. His
general views of this subject, § 239. Explanation of the regular
structure of whinstone hills, according to Dr Hutton's theory, §
240. Many hills supposed to be extinguished volcanoes, are rocks
of real whinstone that has flowed deep under the surface. Vein
of whinstone mistaken for a stream of lava by Faujas, § 241,
242. Submarine volcanoes of Dolomieu, § 243. Objections to this
theory, § 244, 245. Dolomieu in another place contends for the
aqueous formation of basaltes, § 246. His arguments answered;
also those of Bergman, § 248, 249. Argument of WERNER for the
aqueous origin of basaltes, § 250. Remarks on the supposed
gradual transition of basaltes to argillaceous schistus, §
251, 252. Of the shells said to be found in basaltes, § 253.
Instances from Portrush in Ireland, and from Cerigo on the
Coast of Greece, _ib._ and 254,--from the Veronese, § 255.
Objections to the Neptunian formation of whinstone, founded on
the difference between it and the contiguous stratified rocks,
§ 256. On the resemblance of the strata below and above certain
masses of whinstone, § 257. On the irregularity of the thickness
of those masses, § 258. Wedge form masses of whinstone included
between strata, § 259. Consequences of this wedge form, § 260.
Sandstone fragments included in whin, § 261, 262. Bending of
the strata contiguous to whinstone, § 264. Induration, § 265,
266. Charring of coal by whin, § 267. Of the manner in which the
bitumen may have been driven off by heat, § 268. Two kinds of
fossil coke, § 269. Graduation into plumbago, _ib._ and 270. Only
remaining objection obviated by Sir James Hall's experiments, §
271.
NOTE XV.--On Granite.
p. 307
Granite veins of two kinds, § 274. Veins Of which the communication
with large masses of the same stone is not visible: At the Isle
of Coll in the Hebrides, § 275,--at Portsoy, § 276,--in Cornwall,
§ 277,--in Glentilt, § 278. Veins visibly connected with larger
masses. Argument furnished by them in favour of this theory, §
279, 280. Impossibility of their being formed by infiltration, §
281. Veins of this kind in Arran, § 282,--Galloway, § 283,--sides
of Loch Chloney, Invernessshire, §284,--St Michael's Mount,
Cornwall § 285. Fragments of schistus contained in granite, § 287.
2. Granite of Portsoy.
p. 320
Description of this granite, § 288. Pierre graphique of M. Patrin
not perfectly the same with that of Portsoy, § 289. Quartz
crystallized in the pierre graphique, § 290. Instances of quartz
crystallized in other granites. In that of St Agnes in Cornwall,
§ 291. Whether this crystallization is only found in secondary
granites, § 292.
3. Stratification of Granite.
p. 326
Question stated concerning the stratification of granite, § 293.
Remarkable examples of stratified granite at Chorley Forest,
Leicestershire, and at Fassnet _Water_ in Berwickshire, § 295.
Stratification of Mont Blanc, and the Aiguilles of Chamouni
maintained by Saussure, § 296, 297. Seems nevertheless doubtful,
§ 298. In the granite mountains of Arran doubtful; § 300.
Explanation of the stratification of granite in this theory, §
301. If granitic veins were found proceeding from real granitic
strata, they could not be explained on the principles here laid
down, § 302. No such veins have been discovered, § 303. Answer to
an objection made to the igneous origin of granitic mountains, §
304, 305. Of the proportion of the earth's surface occupied by
granite rocks, § 306. Not exceeding a ninetieth part, § 307, 311.
Extent of granite in Scotland erroneously estimated by Dr Hutton,
§ 312. Amounts perhaps to a twenty-fourth of the whole surface, §
313. Observations on Mr Kirwan's opinion, § 314.
NOTE XVI.--Rivers and Lakes.
p. 350
The rivers have hollowed out the valleys, § 315. Illustration
from the course of the Danube, § 316. Courses of many rivers
retain marks of having consisted of a series of lakes, § 317,
318. Filling up and draining of lakes, § 320. Instances from
the lakes in Cumberland, § 321. Lake of Geneva, § 322. Lakes in
North America, _ib._ Cataracts, § 323. Difficulties in explaining
the generation and continuance of lakes exemplified in that of
Geneva, § 324. Attempt to resolve these difficulties, § 325, 326,
327, 328. All lakes not equally subject to them, § 329. Wasting
of the land by the rivers, proved from the mouths of rivers on
bold coasts, § 330. Examples from Cornwall, § 331.
NOTE XVII.--Remains of Decomposed Rocks.
p. 371
Plain of Crau, § 334. Its gravel from the decomposition of
pudding-stone, § 385. Same true of much of the gravel in this
island, § 337, 338. Mount Rigi in Switzerland the remains of a
body of pudding-stone, § 339. Measure of the destruction in the
stratified rocks sometimes, afforded by the unstratified, § 340,
341. Rate at which the elevation of mountains has been supposed
to decrease, § 342.
NOTE XVIII.--Transportation of Stones, &c.
p. 381
Gravel smaller and rounder the farther from its native place, §
343. Different sources of _caillou roulés_, § 344, 345. Stones
that have begun their migration before the cutting out of the
present valleys, § 346. Declivity necessary to enable stones
to travel from the top of Mont Blanc to the top of Mont Jura,
§ 347. Granite from Mont Blanc found eastward in the valley of
the Drance, § 348. Machinery employed by nature in transporting
rocks, § 349, 350. Instances of transported stones of great
size,--from the vicinity of Geneva, § 351, 352,--from the Isle
of Arran, 353. How gravity may contribute to the moving of large
stones, even when the declivity is small, § 354. Rocking-stones,
§ 355. Stone in Borrowdale,--in the valley of Urseren, § 356.
Large stones are sometimes the remains of veins, § 357. Of
the hypothesis of a _debacle_, § 358. Structure of valleys
unfavourable to this hypothesis, § 359, 360. Particularly of
valleys close at the ends, § 361, 362. Whether the supposition of
a _debacle_ is necessary to explain the moving of large masses
of rock, § 364. Whether the abrupt faces of hills indicate the
existence of any sudden torrent, &c. § 365. Fact concerning the
steep faces of the mountains in the south of Africa, § 366. A
fact stated that would lead necessarily to belief in a _debacle_;
no example of it has yet occurred, § 367.
NOTE XIX.--Transportation of Materials
by the Sea.
p. 413
Of the manner in which the _detritus_ of the land is spread out
over the bottom of the sea, § 369, 370. Seas rendered shallower,
§ 371. Sand banks, § 372. Great system of currents traced in the
Atlantic, § 373, 374. How far this transportation of materials
may affect the earth's diurnal motion, § 376, 377. Kirwan's
misapprehension of Frisi, and of Major Rennell, § 378, 379. His
mistake about the tides, § 380, 381,--and about the formation of
sand banks, § 384.
NOTE XX.--Inequalities of the
Planetary Motions.
p. 437
These inequalities all periodical, § 385. Circumstances on which
this depends, § 386. Affinity of this conclusion to that which Dr
Hutton has established with respect to the changes at the surface
of the earth, § 387.
NOTE XXI.--Changes in the Apparent
Level of the Sea.
p. 441
Relative level of the sea and land subject to change, § 388. Proofs
that it has sunk, on the shores of this island, § 389,--on the
coasts of France and Flanders, § 390, 391,--on the shores of the
Baltic, § 392. This has not arisen from the depression of the
sea, but from the elevation of the land, § 393, 394. The surface
of the Hadriatic higher now than formerly, § 395, 396. Also of
the Mediterranean, § 398. Irregularities in these changes, § 399,
400. Hypothesis of Frisi, that towards the equator the sea is
every where rising, § 401. Disproved, _ib._ Conclusion, § 402.
NOTE XXII.--Fossil Bones.
p. 458
Vegetable and animal remains contained in the fossil kingdom, §
403. Of those that are enveloped or penetrated with calcareous
earth, § 405, 406. Of the bones buried in the loose earth,
§ 407. Bones in Siberia referred to the rhinoceros and the
elephant, § 408. Those on the Ohio doubtful, § 408, 409. Opinion
of Camper, § 410.--of Cuvier, § 411. Objections to the latter,
_ib._ Enumeration of five _species_ of animals now extinct, §
412. Change in the animal, and vegetable kingdom may account for
bones found in countries where no analogous species now exists,
§ 414. Proofs that the animals whose bones are found in Siberia
inhabited that country, § 415-417.
NOTE XXIII.--Geology of Kirwan and De Luc.
p. 477
These authors have improperly drawn religion into their quarrel
with Dr Hutton, § 419. De Luc writes a history of what befel the
earth before the creation of the sun, § 420. Remarks on Kirwan's
geological writings, § 422, 423, 424, 425.
NOTE XXIV.--System of Buffon.
p. 483
In what Buffon's theory of the earth and Dr Hutton's agree,
and in what they differ, § 426, 427. Great merit of Buffon,
notwithstanding his errors, § 428.
NOTE XXV.--Figure of the Earth.
p. 488
Physical cause of the earth's oblate figure not obvious from its
present condition, § 429. How explained by the Neptunists, §
430. Examination of their solution, § 431, 432. Contradiction
implied in it, § 433. Insufficiency of Buffon's explanation, §
434. Of the principle on which the oblateness of the earth may
be accounted for in Dr Hutton's theory, § 435. Of the changes
that would happen in the figure of a terraqueous body like the
earth, supposing it ever so irregular, § 436, 437, 438. Two
different causes of change, _ib._ Ultimate figure, that by which
the causes of change are best resisted, § 439. Spheroidal figure,
never perfectly acquired, § 440. Agreement of this theory with
observation, § 441. Probable extension of the system of waste,
and renovation to the other planets, § 442, 443. Confirmation
from the system of Saturn, § 444, 445.
NOTE XXVI.--Prejudices relating to
the Theory of the Earth.
p. 510
Alleged by some that a theory of the earth ought not at present to
be attempted, § 446. The quick succession of geological theories
has partly arisen from their object being misunderstood, § 447. A
succession of theories is often a continued approximation to the
truth, § 448. The more various the phenomena of any class, the
greater the chance of discovering their true cause, § 449. Reason
to think that the leading facts in geology are now known, § 450,
451. A tendency may be observed in geological systems to approach
to one another, and to the Huttonian, § 452. Example from that
of Saussure, § 453,--of Dolomieu, § 454, 455. The discoveries of
Dr Black were necessary for understanding the true theory of the
earth, § 457. Use of theory in matters of observation, § 458, &c.
ILLUSTRATIONS, &c.
A VERY little attention to the phenomena of the mineral kingdom, is
sufficient to convince us, that the condition of the earth's surface
has not been the same at all times that it is at the present moment.
When we observe the impressions of plants in the heart of the hardest
rocks; when we discover trees converted into flint, and entire beds of
limestone or of marble composed of shells and corals; we see the same
individual in two states, the most widely different from one another;
and, in the latter instance, have a clear proof, that the present land
was once deep immersed under the waters of the ocean. If to this we
add, that many masses of rock, the most solid and compact, consist of
no other materials but sand and gravel; that, on the other hand, loose
gravel, such as is formed only in beds of rivers, or on the sea shore,
now abounds in places remote from both: if we reflect, at the same
time, on the irregular and broken figure of our continents, and the
identity of the mineral strata on opposite sides of the same valley, or
the same inlet of the sea; we shall see abundant reason to conclude,
that the earth has been the theatre of many great revolutions, and that
nothing on its surface has been exempted from their effects.
To trace the series of these revolutions, to explain their causes, and
thus to connect together all the indications of change that are found
in the mineral kingdom, is the proper object of a THEORY OF THE EARTH.
But, though the attention of men may be turned to the theory of the
earth by a very superficial acquaintance with the phenomena of geology,
the formation of such a theory requires an accurate and extensive
examination of those phenomena, and is inconsistent with any but a
very advanced state of the physical sciences. There is, perhaps, in
those sciences, no research more arduous than this; none certainly
where the subject is so complex; where the appearances are so extremely
diversified, or so widely scattered, and where the causes that have
operated are so remote from the sphere of ordinary observation. Hence
the attempt! to form a theory of the earth are of very modern origin,
and as, from the simplicity of its subject astronomy is the eldest, so,
on account of the complexness of its subject, geology is the youngest
of the sciences.
It is foreign from the present purpose to enter on any history of
the systems that, since the rise of this branch of science, have
been invented to explain the phenomena of the mineral kingdom. It is
sufficient to remark, that these systems are usually reduced to two
classes, according as they refer the origin of terrestrial bodies
to FIRE or to WATER; and that, conformably to this division, their
followers have of late been distinguished by the fanciful names of
_Vulcanists_ and _Neptunists_. To the former of these Dr Hutton belongs
much more than to the latter; though, as he employs the agency both of
fire and of water in his system, he cannot, in strict propriety, be
arranged with either.
In the succinct account which I am now about to give of this system, I
shall consider the mineral kingdom as divided into two parts, namely,
stratified and unstratified substances I shall treat, first, of the
phenomena peculiar to the stratified; next, of those peculiar to the
unstratified; and, lastly, of the phenomena common to both. Beginning,
then, with the first, the subject naturally divides itself into three
branches; viz. the _materials_ the _consolidation_, and the _position_
of the strata.
SECTION I.
OF THE PHENOMENA PECULIAR TO STRATIFIED BODIES.
1. _Materials of the Strata._
1. IT is well known that, on removing the loose earth which forms the
immediate surface of the land, we come to the solid rock, of which a
great proportion is found to be regularly disposed in strata, or beds
of determinate thickness, inclined at different angles to the horizon,
but separated from one another by equidistant superficies, that often
maintain their parallelism to a great extent. These strata bear such
evident marks of being deposited by water, that they are universally
acknowledged to have had their origin at the bottom of the sea; and
it is also admitted, that the materials which they consist of, were
then either soft, or in such a state of comminution and separation,
as renders them capable of arrangement by the action of the water in
which they were immersed. Thus far most of the theories of the earth
agree; but from this point they begin to diverge, and each to assume
a character and direction peculiar to itself. Dr Hutton's does so, by
laying down this fundamental proposition, That in all the strata we
discover proofs of the materials having existed as elements of bodies,
which must have been destroyed before the formation of those of which
these materials now actually make a part.[1]
[Footnote 1: Hutton's Theory, vol. I p. 20, &c.]
2. The calcareous strata are the portion of the mineral kingdom that
gives the clearest testimony to the truth of this assertion. They often
contain shells, corals, and other exuviæ of marine animals in so great
abundance, that they appear to be composed of no other materials.
Though these remains of organized bodies are now converted into stone
or into spar, their shape and interior structure are often so well
preserved, that the species of animal or plant of which they once made
a part, can still be distinguished and pointed out among the living
inhabitants of the ocean.
Others of the calcareous strata appear to be composed of fragments of
some ancient rocks, which, after having been broken, have been again
united into a compact stone. In these we find pieces clearly marked
as having been once continuous but now placed at a distance from one
another, and exhibiting exactly the same appearances as if they floated
in a fluid of the same specific gravity with themselves.
From these, therefore, and a variety of similar appearances, Dr Hutton
concludes, that the materials of all the calcareous strata have been
furnished, either from the dissolution of former strata, or from the
remains of organized bodies. But, though this conclusion is meant to be
extended to all the calcareous strata, it is not asserted that every
cubic inch of marble or of limestone contains in it the characters of
its former condition, and of the changes through which it has passed.
It may, however, be safely affirmed, that there is scarce any entire
stratum where such characters are not to be found. These must be
held as decisive with respect to the whole system of strata to which
they belong; they prove the existence of calcareous rocks before the
formation of the present; and, as the destruction of those is evidently
adequate to the supply of the materials of these that we now see, to
look for any other supply were superfluous, and could only embarrass
our reasonings by the introduction of unnecessary hypotheses.[2]
[Footnote 2: NOTE I.]
3. The same conclusions result from an examination of the siliceous
strata; under which we may comprehend the common sandstone, and also
those pudding-stones or breccias where the gravel consists of quartz.
In all these instances, it is plain, that the sand or gravel existed in
a state quite loose and unconnected, at the bottom of the sea, previous
to its consolidation into stone. But such bodies of gravel or sand
could only be formed from the attrition of large masses of quartz, or
from the dissolution of such sandstone strata as exist at present; for
it will hardly be alleged, that sand is a crystallization of quartz,
formed from that substance, when it passes from a fluid to a solid
state.
Those pudding-stones in which the gravel is round and polished, carry
the conclusion still farther, as such gravel can only be formed in the
beds of rivers or on the shores of the sea; for, in the depths of the
ocean, though currents are known to exist, yet there can be no motion
of the water sufficiently rapid to produce the attrition required to
give a round figure and smooth surface to hard and irregular pieces
of stone. There must have existed, therefore, not only a sea, but
continents, previously to the formation of the present strata.
The same thing is clearly shown by those petrifactions of wood, where,
though the vegetable structure is perfectly preserved, the whole mass
is siliceous, and has, perhaps, been found in the heart of some
mountain, deep imbedded in the solid rock.
4. Characters of the same import are also found among the argillaceous
strata, though perhaps more rarely than among the calcareous or
siliceous. Such are the impressions of the leaves and stems of
vegetables; also the bodies of fish and amphibious animals, found very
often in the different kinds of argillaceous schistus, and in most
instances having the figure accurately preserved, but the substance
of the animal replaced by clay or pyrites. These are all remains
of ancient seas or continents; the latter of which have long since
disappeared from the surface of the earth, but have still their memory
preserved in those archives, where nature has recorded the revolutions
of the globe.
5. Among bituminous bodies, pit-coal is the only one which constitutes
regular and extensive strata; and no fossil has its origin from the
waste of former continents, marked by stronger and more distinct
characters. Not to mention that the coal strata are alternated with
those that have been already enumerated, and that they often contain
shells and corals, perfectly mineralized, it is sufficient to remark,
that there are entire beds of this fossil, which appear to consist
wholly of wood, and in which the fibrous structure is perfectly
preserved. From these instances, the appearances of vegetable
structure may be traced through all possible gradations, down to an
evanescent state. This last state is undoubtedly the most common; and
though coal does not then, on bare inspection, make known its vegetable
origin, yet, if we take it in connection with the other terms of the
series, as we may call them; if we consider that the two extremes, viz.
coal, with the vegetable structure perfect, and coal without any such
structure visible, are often found in the same or in contiguous beds;
and, if we remark, that through all these gradations coal contains
nearly the same chemical elements, and yields, on analysis, bitumen and
charcoal, combined with a greater or less proportion of earth: if we
take all these circumstances into account, we cannot doubt that this
fossil is every where the same, and derives its origin from the trees
and plants that grew on the surface of the earth before the formation
of the present land.
6. Dr Hutton has further observed, that if those ancient continents
were at all similar to the present, we can be at no loss to account for
the want of any distinct mark of vegetable organization in the greater
part of the coal strata. It is plain, that the daily waste of animal
and vegetable substances on the surface of the earth, must disengage
a great quantity of oily as well as carbonic matter, which, with
whatever element it is at first combined, is ultimately delivered into
the ocean. Thus, the oily or fuliginous parts of animal and vegetable
substances, let loose by burning, first ascend into the atmosphere, but
are at length precipitated, and either fall immediately into the sea,
or are, in part at least, washed down into it from the land. From other
causes also, much vegetable matter is carried down by the rivers; and
the whole quantity of animal and vegetable substances thus delivered
into the sea, must be very considerable, amounting annually to the
whole residuum of those substances, not employed in the maintenance or
reproduction of animal and vegetable bodies. Whether chemically united
to the waters of the ocean, or simply suspended in them, this matter is
at last precipitated, and, mingling with earthy substances, is formed
into strata, the place of which will be determined by the currents, the
position of the present continents, and many other circumstances not
easily enumerated.
If, then, an order of things similar to what we now see, existed before
the formation of the present strata, it would necessarily happen, that
the animal and vegetable substances, diffused through the ocean, being
separated from the water, would be deposited at the bottom of the
sea, and, in the course of ages, would form beds, less or more pure,
according to the quantity of earth and other substances deposited
at the same time. These beds being consolidated and mineralized by
operations that are afterwards to be considered, have been converted
into pit-coal, the parts of which are impalpable, and retain nothing of
their primitive structure.[3]
[Footnote 3: NOTE II.]
If, then, the formation of coal from animal and vegetable bodies be
admitted, the general position which derives the origin of the strata
from the waste of former land, as it is applicable to all the kinds
already enumerated, and of course to all those with which they are
alternated, comprehends a very large portion of the earth's surface.
It comprehends, indeed, all the strata usually distinguished by the
name of _Secondary_; but there is another great division of the mineral
kingdom, viz. the rocks, called _Primitive_, which, as they are never
alternated with the secondary, but are always inferior to them, must
be further examined, before we can decide whether the same conclusion
extends to them or not.
7. Here it must be carefully observed, that, among the primary rocks,
the granite is not meant to be included, except where that stone is
stratified, and either coincides with veined granite or with gneiss.
The primitive strata, in Dr Hutton's theory, comprehend, besides
gneiss, the micaceous, chlorite, hornblende, and siliceous schistus,
together with slate, and some other kinds of argillite; to which we
must add, serpentine, micaceous limestone, and the greater part of
marbles. These are mostly distinguished by their laminated structure,
by having their planes much elevated with respect to the horizon,
and by belonging more to the mountainous than the level parts of the
earth's surface. They rarely contain vestiges of organized bodies;
so rarely, indeed, that they were called primitive by the geologists
who first distinguished them from other rocks, on the supposition of
their being part of the primeval nucleus of the globe, which had never
undergone any change whatsoever; but this, I believe, has now almost
ceased to be the opinion of any geologist.[4] The Neptunists hold the
rocks, here enumerated, and also granite, to be produced by aqueous
deposition; but maintain them to be in the strictest sense primeval,
and of a formation antecedent to all organized bodies.
[Footnote 4: NOTE III.]
8. In opposition to this, Dr Hutton maintained, that the primary
schistus, like all the other strata, was formed of materials deposited
at the bottom of the sea, and collected from the waste of rocks still
more ancient. When, therefore, he conformed to the received language
of mineralogists, by calling these strata primitive, he only meant
to describe them as more ancient than any other strata now existing,
but not as more ancient than any that ever had existed. They are
distinguished, in his system, by the name of _Primary_, rather than of
_Primitive_ strata.
That the account now given of their origin is well founded, may be
proved by unquestionable facts. For, first, though, agreeably to the
observation just made, the ancient strata do but rarely contain any
remains of organized bodies, they are not entirely destitute of them.
Different places in this island have been pointed out by Dr Hutton,
where marine objects have been discovered in primary limestone, either
by himself or others, and it would not be difficult to add more
instances of the same kind.[5] In Dauphine, coal, which is certainly a
derivative substance, has been found among mountains which have a title
to the character of primitive, such as no one will dispute. These facts
put the composition of such rocks from loose materials, beyond all
doubt, and also prove their formation to be posterior to the existence
of an animal and vegetable system. They do indeed prove this in the
strictest sense, only of the particular beds in which they are found;
but as these beds are in all other respects as much to be accounted
primary as any part of the mineral kingdom, it is evident that the
negative instances are here of no force, and that nothing can be gained
to the adversaries of this opinion by denying it in general, if they
are obliged to admit it in a single case.
[Footnote 5: NOTE IV.]
9. Again, it is certain, as Dr Hutton remarks, that there are few
considerable bodies of schistus, even the most decidedly primitive,
where sand and gravel may not in some parts be observed. Indeed, it is
not only true that they are to be found in some parts of them; but,
in fact, among many of the primitive mountains, we find large tracts,
composed entirely of a schistose and much indurated sandstone, in beds
highly inclined, sometimes alone, sometimes alternated with other
schisti. In many of them, the sand of which they consist appears to be
entirely of granite, from the detritus of which rock it should seem
that they were chiefly formed.
10. Thus we conclude, that the strata both primary and secondary,
both those of ancient and those of more recent origin, have had their
materials furnished from the ruins of former continents, from the
dissolution of rocks, or the destruction of animal or vegetable
bodies, similar, at least in some respects, to those that now occupy
the surface of the earth. This conclusion is not indeed proved of every
individual portion of rock, but it is demonstrated of many and large
parts, and those scattered indifferently through all the varieties of
the strata; and therefore, from the rules of the strictest reasoning,
we must infer, that the whole is derived from the same origin.[6]
[Footnote 6: NOTE V.]
Thus far concerning the materials of the strata; and, as these were
originally loose and unconnected, we must next consider by what means
they were consolidated into stone.
2. _Consolidation of the Strata_.
11. Though Dr Hutton has no where defined the meaning of the term
consolidation, he has been scrupulously exact in using it constantly
in the same sense. He understands by it, not merely that quality in a
hard body, by which its parts cohere together, but also that by which
it fills up the space comprehended within its surface, being to sense
without porosity, and impervious to air and moisture.
Now, a porous mass of unconnected materials, such as the strata appear
originally to have been, can acquire hardness and solidity only in two
ways, that is, either when it is first reduced by heat into a state of
fusion, or at least of softness, and afterwards permitted to cool; or
when matter that is dissolved in some fluid menstruum, is introduced
along with that menstruum into the porous mass, and, being deposited,
forms a cement by which the whole is rendered firm and compact. Fire
and water, therefore, are the only two physical agents to which we can
ascribe the consolidation of the strata; and, in order to determine to
which of them that effect is to be attributed, we must inquire whether
there are any certain characters that distinguish the action of the one
from that of the other, and which may be compared with the phenomena
actually observed among mineral substances.
12. First, then, it is evident, that the consolidation produced by the
action of water, or of another fluid menstruum, in the manner just
referred to, must necessarily be imperfect, and can never entirely
banish the porosity of the mass. For the bulk of the solvent, and of
the matter it contained in solution, being greater than the bulk of
either taken singly, when the latter was deposited, the former would
have sufficient room left, and would continue to occupy a certain
space in the interior of the strata. A liquid solvent, therefore, could
never shut up the pores of a body to the entire exclusion of itself;
and, had mineral substances been consolidated, as here supposed, the
solvent ought either to remain within them in a liquid state, or if
evaporated, should have left the pores empty and the body pervious to
water. Neither of these however, is the fact; many stratified bodies
are perfectly impervious to water, and few mineral substances contain
water in a liquid state. That they sometimes contain it, chemically
united to them, is no proof of their solidity having been brought
about by that fluid; for such chemical union is as consistent with the
supposition of igneous as of aqueous consolidation, since the region in
which the fire was applied, on every hypothesis must have abounded with
humidity.
13. Again, if water was the solvent by which the consolidating matter
was introduced into the interstices of the strata, that matter could
consist only of such substances as are soluble in water, whereas
it consists of a vast variety of substances, altogether insoluble
either in it, or in any single menstruum whatsoever. The strata are
consolidated, for example, by quartz, by fluor, by feldspar, and by all
the metals, in their endless combinations with sulphureous bodies. To
affirm that water was ever capable of dissolving these substances, is
to ascribe to it powers which it confessedly has not at present; and,
therefore, it is to introduce an hypothesis, not merely gratuitous, but
one which, physically speaking, is absurd and impossible.
This is not all, however; for, even if this difficulty were to be
passed over, it would still be required to explain, how the water,
which, together with the matter which it held in solution, had
insinuated itself into the pores of the strata, became suddenly
disposed to deposit that matter, and to allow it, by crystallization
or concretion, to assume a solid form.[7] The Neptunists must either
assign a sufficient reason for this great and universal change, or must
expect to see their system treated as an inartificial accumulation
of hypotheses which assigns opposite virtues to the same subject,
and is alike at variance with nature and with itself; in a word, a
system that might pass for the invention of an age, when as yet sound
philosophy had not alighted on the earth, nor taught man that he is
but the minister and interpreter of nature, and can neither extend his
power nor his knowledge a hair's-breadth beyond his experience and
observation of the present order of things.[8]
[Footnote 7: NOTE VI.]
[Footnote 8: Homo naturæ minister, et interpres tantùm facit et
intelligit, quantùm de naturæ ordine re, vel mente, observaverit: nec
amplius scit, aut potest.--Nov. Org. lib. i. aph. 1.]
14. Such are the more obvious, but I think unanswerable objections,
that may be urged against the aqueous consolidation of the strata.
It is true, that stony concretions, some of them much indurated, are
formed in the humid way under our eyes. Very particular conditions,
however, are required for that purpose, and conditions such as can
hardly have existed at the bottom of the sea. First. The water must
dissolve the substance of which the concretion is to be formed, as it
actually does in the case of calcareous, and in certain circumstances,
in that of siliceous, earth. Secondly. It must be separated from
that substance, as by evaporation, or by a combination of the matter
dissolved with some third substance, to which it has a greater affinity
than to water, so as to form with it an insoluble compound. Lastly,
the water that is deprived of its solution must be carried off, and
more of that which contains the solution must be supplied, as sometimes
happens where water runs in a stream, or drops from the roof of a
cavern. The two last conditions are peculiarly inapplicable to the
bottom of the sea, where the state of the surrounding fluid would
neither permit the water that was deprived of its solution from being
drawn off, nor that which contained the solution from succeeding it.
It is further to be observed, that the consolidation of stalactitical
concretions, that is, the filling up of their pores, is always
imperfect, and is brought about by the repeated action of the fluid
running through the porous mass, and continuing to deposit there
some of the matter it holds in solution. This, which is properly
infiltration, is incompatible with the nature of a fluid, either
nearly, or altogether quiescent.
15. In order to judge whether objections of equal weight can be opposed
to the hypothesis of igneous consolidation, we must attend to a very
important remark, first made by Dr Hutton, and applied with wonderful
success to explain the most mysterious phenomena of the mineral kingdom.
It is certain, that the effects of fire on bodies vary with the
circumstances under which it is applied to them, and, therefore, a
considerable allowance must be made, if we would compare the operation
of that element when it consolidated the strata, with the results of
our daily experience. The materials of the strata were disposed, as we
have already seen, loose and unconnected, at the bottom of the sea;
that is, even on the most moderate estimation, at the depth of several
miles under its surface. At this depth, and under the pressure of a
column of water of so great a height, the action of heat would differ
much from that which we observe here upon the surface; and, though
our experience does not enable us to compute with accuracy the amount
of this difference, it nevertheless points out the direction in which
it must lie, and even marks certain limits to which it would probably
extend.
The tendency of an increased pressure on the bodies to which heat is
applied, is to restrain the volatility of those parts which otherwise
would make their escape, and to force them to endure a more intense
action of heat. At a certain depth under the surface of the sea, the
power even of a very intense heat might therefore be unable to drive
off the oily or bituminous parts from the inflammable matter there
deposited, so that, when the heat was withdrawn, these principles
might be found still united to the earthy and carbonic parts, forming
a substance very unlike the residuum obtained after combustion under
a pressure no greater than the weight of the atmosphere. It is in
like manner reasonable to believe, that, on the application of heat
to calcareous bodies under great compression, the carbonic gas would
be forced to remain; the generation of quicklime would be prevented,
and the whole might be softened, or even completely melted; which last
effect, though not directly deducible from any experiment yet made, is
rendered very probable, from the analogy of certain chemical phenomena.
16. An analogy of this kind, derived from a property of the barytic
earth, was suggested by that excellent chemist and philosopher, the
late Dr BLACK. The barytic earth, as is well known, has a stronger
attraction for fixed air than common calcareous earth has, so that the
carbonate of barytes is able to endure a great degree of heat before
its fixed air is expelled. Accordingly, when exposed to an increasing
heat, at a certain temperature, it is brought into fusion, the fixed
air still remaining united to it: if the heat be further increased,
the air is driven off, the earth loses its fluidity, and appears in
a caustic state. Here, it is plain, that the barytic earth, which is
infusible, or very refractory, _per se_, as well as the calcareous,
owes its fusibility to the presence of the fixed air; and it is
therefore probable, that the same thing would happen to the calcareous
earth, if by any means the fixed air were prevented from escaping when
great heat is applied to it. This escape of the fixed air is exactly
what the compression in the subterraneous regions is calculated to
prevent, and therefore we are not to wonder if, among the calcareous
strata, we find marks of actual fusion having taken place.[9]
[Footnote 9: NOTE VII.]
17. These effects of pressure to resist the decomposition, and augment
the fusibility of bodies, being once supposed, we shall find little
difficulty in conceiving the consolidation of the strata by heat, since
the intervals between the loose materials of which they originally
consisted may have been closed, either by the softening of those
materials, or by the introduction of foreign matter among them, in
the state of a fluid, or of an elastic vapour. No objection to this
hypothesis can arise from the considerations stated in the preceding
case; the solvent here employed would want no pores to lodge in after
its work was completed, nor would it find any difficulty in making its
retreat through the densest and most solid substances in the mineral
kingdom. Neither can its incapacity to dissolve the bodies submitted
to its action be alleged. Heat is the most powerful and most general
of all solvents; and, though some bodies, such as the calcareous, are
able to resist its force on the surface of the earth, yet, as has just
been shown, it is perfectly agreeable to analogy to suppose, that,
under great pressure, the carbonic state of the lime being preserved,
the purest limestone or marble might be softened, or even melted.
With respect to other substances, less doubt of their fusibility is
entertained; and though, in our experiments, the refractory nature of
siliceous earth has not been completely subdued, a degree of softness
and an incipient fusion have nevertheless been induced.
Thus it appears, in general, that the same difficulties do not press
against the two theories of aqueous and of igneous consolidation; and,
that the latter employs an agent incomparably more powerful than the
former, of more general activity, and, what is of infinite importance
in a philosophical theory, vastly more definite in the laws of its
operation.
18. A more particular examination of the different kinds of fossils
will confirm this conclusion, and will show, that, wherever they bear
marks of having been fluid, these marks are such as characterize the
fluidity of fusion, and distinguish it from that which is produced
by solution in a menstruum. Dr Hutton has enumerated many of these
discovered in the course of that careful and accurate examination of
fossils, in which he probably never was excelled by any mineralogist.
It will be sufficient here to point out a few of the most remarkable
examples.
19. Fossil wood, penetrated by siliceous matter, is a substance well
known to mineralogists; it is found in great abundance in various
situations, and frequently in the heart of great bodies of rock. On
examination, the siliceous matter is often observed to have penetrated
the wood very unequally, so that the vegetable structure remains in
some places entire; and in other places is lost in a homogeneous mass
of agate or jasper. Where this happens, it may be remarked, that the
line which separates these two parts is quite sharp and distinct,
altogether different from what must have taken place, had the flinty
matter been introduced into the body of the wood, by any fluid in which
it was dissolved, as it would then have pervaded the whole, if not
uniformly, yet with a regular gradation. In those specimens of fossil
wood that are partly penetrated by agate, and partly not penetrated
at all, the same sharpness of termination may be remarked, and is an
appearance highly characteristic of the fluidity produced by fusion.
20. The round nodules of flint that are found in chalk, quite insulated
and separate from one another, afford an argument of the same kind;
since the flinty matter, if it had been carried into the chalk by any
solvent, must have been deposited with a certain degree of uniformity,
and would not now appear collected into separate masses, without any
trace of its existence in the intermediate parts. On the other hand, if
we conceive the melted flint to have been forcibly injected among the
chalk, and to have penetrated it, somewhat as mercury may, by pressure,
be made to penetrate through the pores of wood, it might, on cooling,
exhibit the same appearances that the chalk-beds of England do actually
present us with.
The siliceous pudding-stone is an instance closely connected with the
two last; in it we find both the pebbles, and the cement which unites
them, consisting of flint equally hard and consolidated; and this
circumstance, for which it is impossible to account by infiltration, or
the insinuation of an aqueous solvent, is perfectly consistent with the
supposition, that a stream of melted flint has been forcibly injected
among a mass of loose gravel.
21. The common grit, or sandstone, though it certainly gives no
indication of having possessed fluidity, is strongly expressive of the
effects of heat. It is so, especially in those instances where the
particles of quartzy sand, of which it is composed, are firmly and
closely united, without the help of any cementing substance whatsoever.
This appearance, which is very common, seems to be quite inconsistent
with every idea of consolidation, except an incipient fusion, which,
with the assistance of a suitable compression, has enabled the
particles of quartz to unite into stone.
It has indeed been asserted, that the mere apposition of stony
particles, so as to permit their corpuscular attraction to take place,
was sufficient to form them into stone. To this Dr Hutton has very well
replied, that, admitting the possibility of a hard and firm body being
produced in this way of which, however, we have no proof, the close
and compact texture, the perfect consolidation of the stones we are
now speaking of, would still remain to be explained, and of this it is
evident that the mere apposition of particles, and the force of their
mutual attraction, can afford no solution.
22. These proofs that the strata must have endured the action of
intense heat, though immediately deduced from those of the siliceous
genus only, extend in reality to all the strata, of every kind, with
which they are found alternated. It is impossible that heat, of the
intensity here supposed, can have acted on a particular stratum, and
not on those that are contiguous to it; and, as there are no strata of
any kind with which the quartzy and siliceous are not intermixed, so
there are none of which the igneous consolidation is not thus rendered
probable. We need rest nothing, however, on this argument, as the
fossils of every genus may be shown to speak distinctly for themselves.
23. Those of the calcareous genus do so perhaps more sparingly than
the rest; yet even among them there are many facts, that, though taken
unconnected with all others, are sufficient to establish the action of
subterraneous fire. Such, for example, are the calcareous breccias,
composed of fragments of marble or limestone, and not only adapted to
each other's shape, but indented into one another, in a manner not
a little resembling the _sutures_ of the human _cranium_. From such
instances, it is impossible not to infer the softness of the calcareous
fragments when they were consolidated into one mass. Now, this softness
could be induced only by heat; for it must be acknowledged, that the
action of any other solvent is quite inadequate to the softening of
large fragments of stone, without dissolving them altogether.
24. In many other instances it appears certain, that the stones
of the calcareous genus have been reduced by heat into a state of
fluidity much more perfect. Thus, the saline or finer kinds of marble,
and many others that have a structure highly crystallized, must
have been softened to a degree little short of fusion, before this
crystallization could take place. Even the petrifactions which abound
so much in limestones tend to establish the same fact; for they possess
a sparry structure, and must have acquired that structure in their
transition from a fluid to a solid state.[10]
[Footnote 10: NOTE VIII.]
25. In accounting, by the operation of heat, for these appearances
of fluidity, Dr Hutton has proceeded on the principle already laid
down, as conformable to analogy, that calcareous earth, under great
compression, may have its fixed air retained in it, notwithstanding the
action of intense heat, and may, by that means, be reduced into fusion,
or into a state approaching to it. In all this I do not think that he
has departed from the strictest rules of philosophical investigation.
The facts just stated prove, that limestone was once soft, its
fragments retaining at the same time their peculiar form, an effect to
which we know of none similar but those of fire; and, therefore, though
we could not conjecture how heat might be applied to limestone so as
to melt it, instead of reducing it to a calx, we should, nevertheless,
have been forced to suppose, that this had actually taken place in the
bowels of the earth; and was a fact which, though we were not able to
explain it, we were not entitled to deny. The principle just mentioned
relieves us therefore from a difficulty, that would have embarrassed,
but could not have overturned, this theory of the earth.
26. From the arguments which the argillaceous strata afford for the
igneous consolidation of fossils, I shall select one on which Dr Hutton
used to lay considerable stress, and which some of the adversaries of
his system have endeavoured to refute. This argument is founded on the
structure of certain ironstones called _septaria_, often met with among
the argillaceous schistus, particularly in the vicinity of coal. These
stones are usually of a lenticular or spheroidal form, and are divided
in their interior into distinct _septa_, by veins of calcareous spar,
of which one set are circular and concentric, the other rectilineal;
diverging from the centre of the former, and diminishing in size as
they recede from it. Now, what is chiefly to be remarked is, that
these veins terminate before they reach the surface of the stone; so
that the matter with which they are filled cannot have been introduced
from without by infiltration, or in any other way whatsoever. The only
other supposition, therefore, that is left for explaining the singular
structure of this fossil, is, that the whole mass was originally
fluid, and that, in cooling, the calcareous part separated from the
rest, and afterwards crystallized.
27. It has been urged against this theory of the septaria, that these
stones are sometimes found with the calcareous veins extending all
the way to the circumference, and of course communicating with the
outside. But it must be observed, that this fact does not affect the
argument drawn from specimens in which no such communication takes
place. It is at best only an ambiguous instance, that may be explained
by two opposite theories, and may be reconciled either to the notion
of igneous or of aqueous consolidation: but if there is a single close
septarium in nature, it can, of course, be explained only by one of
these theories, and the other must, of necessity, be rejected. Besides,
it is plain, that a close septarium can never have been open, though an
open septarium may very well have been close; and indeed, as this stone
is, in certain circumstances, subject to perpetual exfoliation, it
would be wonderful if no one was ever found with the calcareous veins
reaching to the surface. With regard to the light, therefore, that they
give into their own history, these two kinds of septaria are by no
means on an equal footing; and this may serve to show, how necessary
it is, in all inductive reasoning, and particularly in a subject so
complex as geology, to separate with care such phenomena as admit of
two solutions, from such as admit only of one.
28. The bituminous strata come next to be considered; and they are of
great consequence in the present argument, because their dissimilarity
in so many particulars to all other mineral substances, renders them
what Lord Bacon calls an _instantia singularis_, having the first
rank among facts subservient to inductive investigation. But though
unlike in substance to other fossils, and composed, as has been shown,
of materials that belonged not originally to the mineral kingdom,
they agree in many material circumstances with the strata already
enumerated. Their beds are disposed in the same manner, and are
alternated indiscriminately with those of all the secondary rocks,
and, being formed in the same region, must have been subject to the
same accidents, and have endured the operation of the same causes.
They are traversed too like the other strata, by veins of the metals,
of spars, of basaltes, and of other substances; and, whatever argument
may hereafter be derived from this to prove the action of fire on the
strata so traversed, is as much applicable to coal as to any other
mineral. The coal strata also contain pyrites in great abundance, a
substance that is perhaps, more than any other, the decided progeny of
fire. This compound of metal and sulphur, which is found in mineral
bodies of every kind, I believe, without any exception, is destroyed
by the contact of moisture, and resolved into a vitriolic salt. At
the same time it is found in the strata, not traversing them in
veins, which may be supposed of more recent formation than the strata
themselves; but existing in the heart of the most solid rocks, often
nicely crystallized, and completely inclosed, on all sides, without the
most minute vacuity. The pyrites must have been present, therefore,
when the strata were consolidated, and it is inconceivable, if their
consolidation was brought about in the wet way, that a substance
should be so generally found in them, the very existence of which is
incompatible with humidity. This argument for the igneous origin of the
strata is applicable to them all, but especially to those of coal, as
abounding with pyrites more than any other.
29. The difficulty that here naturally present itself, viz. how
vegetable matter, such as coal is supposed to have been, could be
exposed to the action of intense heat, without being deprived of its
inflammable part, is obviated by the principle formerly explained
concerning the effects of compression. The weight incumbent on
the strata of coal, when they were exposed to the intense heat of
the mineral regions, may have been such as to retain the oily and
bituminous, as well as sulphureous parts, though the whole was reduced
almost to fusion; and thus, on cooling, the sulphur uniting with iron
might crystallize, and assume the form of pyrites.
30. The compression, however, has not in every instance preserved the
bituminous, in union with the carbonic part of coal; and hence a mark
of the operation of fire quite peculiar to this fossil, and found in
those infusible kinds of it which contain no bitumen, and burn without
flame. These resemble, some of them very precisely, and all them in a
great degree, the products obtained by the distillation of the common
bituminous coal that is, they consist of charcoal, united to an earthy
basis in different proportions. It is natural therefore to conclude,
that this substance was prepared in the mineral regions by the action
of heat, which, in some instances, has driven off the inflammable part
of the coal. That the heat should, in some cases, have done so, is not
inconsistent with the general effect attributed to compression. The
conditions necessary for retaining the more volatile parts, may not
have been present every where in the same degree, so that the latter,
though they could not escape, may have been forced from one part of a
stratum, or body of strata, to another.
31. In confirmation of this it must be observed, that, as the fixed
part of coal is thus found in the bowels of the earth, separate from
the volatile or bituminous, so, in the neighbourhood of coal strata,
the latter is sometimes found without any mixture of the former. The
fountains of naphtha and petroleum are well known; and Dr Hutton
has described a stratum of limestone, lying in the centre of a coal
country, which is pervaded and tinged by bituminous matter, through
its whole mass, and has, at the same time, many close cavities in
the heart of it, lined with calcareous spar, and containing fossil
pitch, sometimes in large pieces, sometimes in hemispherical drops,
scattered over the surface of the cavities. This combination could
only be effected by a part of the inflammable matter of the beds of
coal underneath, being driven off by heat, and made to penetrate the
limestone, while it was yet soft and pervious to heated vapours.[11]
[Footnote 11: NOTE IX.]
32. Hitherto we have enumerated those fossils that are either not at
all, or very sparingly soluble in water. There are, however, saline
bodies among the mineral strata, such for instance as rock-salt, which
are readily dissolved in water; and it yet remains to examine by what
cause their consolidation has been effected.
Here the theorists who consider water as the sole agent in the
mineralization of fossils, are indeed delivered from one difficulty,
but it is only that they may be harder pressed on by another. It
cannot now be said, that the menstruum which they employ is incapable
of dissolving the substances exposed to its action, as in the case of
metallic or stony bodies; but it may very well be asked, how the water
came to deposit the salts which it held in solution, and to deposit
them so copiously as it has done in many places, without any vestige
of similar deposition in the places immediately contiguous. If they
refuse to call to their assistance any other than their favourite
element, they will not find it easy to answer this question, and must
feel the embarrassment of a system, subject to two difficulties, so
nicely, but so unhappily adjusted, that one of them is always prepared
to act whenever the other is removed. If, on the other hand, they will
admit the operation of subterraneous heat, it appears possible, that
the local application of such heat may have driven the water, in
vapour, from one place to another, and by such action often repeated in
the same spot, may have produced those great accumulations of saline
matter, that are actually found in the bowels of the earth.
33. But granting that, either in the way just pointed out, or in some
other that is unknown, the salt and the water have been separated,
some further action of heat seems requisite, before a compact, and
highly indurated body, like rock-salt, could be produced. The mere
precipitation of the salt, would, as Dr Hutton has observed, form only
an assemblage of loose crystals at the bottom of the sea, without
solidity or cohesion: and to convert such a mass into a firm and solid
rock, would require the application of such heat as was able to reduce
it into fusion. The consolidation of rock-salt, therefore, however its
separation from the water is accounted for, cannot be explained but on
the hypothesis of subterraneous heat.
34. Some other phenomena that have been observed in salt mines, come
in support of the same conclusion. The salt rock of Cheshire, which
lies in thick beds, interposed between strata of an argillaceous or
marly stone, and is itself mixed with a considerable portion of the
same earth, exhibits a very great peculiarity in its structure. Though
it forms a mass extremely compact, the salt is found to be arranged
in round masses of five or six feet in diameter, not truly spherical,
but each compressed by those that surround it, so as to have the shape
of an irregular polyhedron. These are formed of concentric coats,
distinguishable from one another by their colour, that is, probably
by the greater or less quantity of earth which they contain, so that
the roof of the mine, as it exhibits a horizontal section of them,
is divided into polygonal figures, each with a multitude of polygons
within it, having altogether no inconsiderable resemblance to a
_mosaic_ pavement. In the triangular spaces without the polygons, the
salt is in coats parallel to the sides of the polygons.
The circumstances which gave rise to this singular structure we should
in vain endeavour to define; yet some general conclusions concerning
them seem to be within our reach. It is clear that the whole mass of
salt was fluid at once, and that the forces, whatever they were, which
gave solidity to it, and produced the new arrangement of its particles,
were all in action at the same time. The uniformity of the coated
structure is a proof of this, and, above all, the compression of the
polyhedra, which is always mutual, the flat side of one being turned to
the flat side of another, and never an angle to an angle, nor an angle
to a side. The coats formed as it were round so many different centres
of attraction, is also an appearance quite inconsistent with the notion
of deposition; both these, however, are compatible with the notion of
solidity acquired by the refrigeration of a fluid, where the whole
mass is acted on at the same time, and where no solvent remains to be
disposed of after the induration of the rest.
35. Another species of fossil salt exhibits appearances equally
favourable to the theory of igneous consolidation. This is the Trona of
Africa, which is no other than soda, or mineral alkali, in a particular
state. The specimen of this fossil in Dr Black's, now Dr Hope's,
collection, is of a sparry and radiated structure, and is evidently
part of the contents of a vein, having a stony crust adhering to it,
on one side, with its own sparry structure complete, on the opposite.
It contains but about one sixth of the water of crystallization
essential to this salt when obtained in the humid way; and, what is
particularly to be remarked, it does not lose this water, nor become
covered with a powder, like the common alkali, by simple exposure to
the air. It is evident, therefore, that this fossil does not originate
from mere precipitation; and when we add, that in its sparry structure
it contains evident marks of having once been fluid, we have little
reason to entertain much doubt concerning the principle of its
consolidation.
Thus, then, the testimony given to the operation of fire, or heat,
as the consolidating power of the mineral kingdom, is not confined
to a few fossils, but is general over all the strata. How far the
unstratified fossils agree in supporting the same conclusion, will be
afterwards examined.
3. _Position of the Strata._[12]
[Footnote 12: Theory of the Earth, vol. i. p. 120.]
36. We have seen of what materials the strata are composed, and by
what power they have been consolidated; we are next to inquire, from
what cause it proceeds, that they are now so far removed from the
region which they originally occupied, and wherefore, from being all
covered by the ocean, they are at present raised in many places fifteen
thousand feet above its surface. Whether this great change of relative
place can be best accounted for by the depression of the sea, or the
elevation of the strata themselves, remains to be considered.
Of these two suppositions, the former, at first sight, seems
undoubtedly the most probable, and we feel less reluctance to suppose,
that a fluid, so unstable as the ocean, has undergone the great
revolution here referred to, than that the solid foundations of the
land have moved a single fathom from their place. This, however, is a
mere illusion. Such a depression of the level of the sea as is here
supposed, could not happen without a change proportionally great in the
solid part of the globe; and, though admitted as true, will be found
very inadequate to explain the present condition of the strata.
37. Supposing the appearances which clearly indicate submersion under
water to reach no higher than ten thousand feet above the present level
of the sea, and of course the surface of the sea to have been formerly
higher by that quantity than it is now; it necessarily follows, that
a bulk of water has disappeared, equal to more than a seven hundredth
part of the whole magnitude of the globe.[13] The existence of empty
caverns of extent sufficient to contain this vast body of water, and of
such a convulsion as to lay them open, and give room to the retreat of
the sea, are suppositions which a philosopher could only be justified
in admitting, if they promised to furnish a very complete explanation
of appearances. But this justification is entirely wanting in the
present case; for the retreat of the ocean to a lower level, furnishes
a very partial and imperfect explanation of the phenomena of geology.
It will not explain the numberless remains of ancient continents that
are involved, as we have seen, in the present, unless it be supposed
that the ancient ocean, though it rose to so great a height, had
nevertheless its shores, and was the boundary of land still higher than
itself. And, as to that which is now more immediately the object of
inquiry, the position of the strata, though the above hypothesis would
account in some sort for the change of their place, relatively to the
level of the sea; yet, if it shall be proved, that the strata have
changed their place relatively to each other, and relatively to the
plane of the horizon, so as to have had an angular motion impressed on
them, it is evident that, for these facts, the retreat of the sea does
not afford even the shadow of a theory.
[Footnote 13: NOTE X.]
38. Now, it is certain, that many of the strata have been moved
angularly, because that, in their original position, they must have
been all nearly horizontal. Loose materials, such as sand and gravel
subsiding at the bottom of the sea, and having their interstices filled
with water, possess a kind of fluidity: they are disposed to yield
on the side opposite to that where the pressure is greatest, and are
therefore, in some degree, subject to the laws of hydrostatics. On
this account they will arrange themselves in horizontal layers; and
the vibrations of the incumbent fluid, by impressing slight motion
backward, and forward, on the materials of these layers, will very much
assist the accuracy of their level.
It is not, however, meant to deny, that the form of the bottom might
influence, in a certain degree, the stratification of the substances
deposited on it. The figure of the lower beds deposited on an uneven
surface, would necessarily be affected by two causes; the inclination
of that surface, on the one hand, and the tendency to horizontality,
on the other; but, as the former cause would grow less powerful as the
distance from the bottom increased, the latter cause would finally
prevail, so that the upper beds would approach to horizontally, and the
lower would neither be exactly parallel to them, nor to one another.
Whenever, therefore, we meet with rocks, disposed in layers quite
parallel to one another, we may rest assured, that the inequalities of
the bottom have had no effect, and that no cause has interrupted the
statical tendency above explained.
Now, rocks having their layers exactly parallel, are very common, and
prove their original horizontally to have been more precise than we
could venture to conclude from analogy alone. In beds of sandstone,
for instance, nothing is more frequent than to see the thin layers of
sand, separated from one another by layers still finer of coaly, or
micaceous matter, that are almost exactly parallel, and continue so to
a great extent without any sensible deviation. These planes can have
acquired their parallelism only in consequence of the property of water
just stated, by which it renders the surfaces of the layers, which it
deposits, parallel to its own surface, and therefore parallel to one
another. Though such strata, therefore, may not now be horizontal, they
must have been so originally; otherwise it is impossible to discover
any cause for their parallelism, or any rule by which it can have been
produced.
39. This argument for the original horizontality of the strata,
is applicable to those that are now farthest removed from that
position. Among such, for instance, as are highly inclined, or even
quite vertical, and among those that are bent and incurvated in the
most fantastical manner, as happens more especially in the primary
schisti, we observe, through all their sinuosities and inflections,
an equality of thickness and of distance among their component
laminæ. This equality could only be produced by those laminæ having
been originally spread out on a flat and level surface, from which
situation, therefore, they must afterwards have been lifted up by the
action of some powerful cause, and must have suffered this disturbance
while they were yet in a certain degree flexible and ductile. Though
the primary direction of the force which thus elevated them must have
been from below upwards, yet it has been so combined with the gravity
and resistance of the mass to which it was applied, as to create a
lateral and oblique thrust, and to produce those contortions of the
strata, which, when on the great scale, are among the most striking and
instructive phenomena of geology.
40. Great additional force is given to this argument, in many cases, by
the nature of the materials of which the stratified rocks are composed.
The beds of breccia and pudding-stone, for instance, are often in
planes almost vertical, and, at the same time, contain gravel-stones,
and other fragments of rock, of such a size and weight, that they
could not remain in their present position an instant, if the cement
which unites them were to become soft; and therefore they certainly
had not that position at the time when this cement was actually soft.
This remark has been made by mineralogists who were not led to it by
any system. The judicious and indefatigable observer of the Alps,
describing the pudding-stone of Valorsine, near the sources of the
Arve, tells us, that he was astonished to find it in beds almost
vertical, a situation in which it could not possibly have been formed.
"That particles," he adds, "of extreme tenuity, suspended in a fluid,
might become agglutinated, and form vertical beds, is a thing that
may be conceived; but that pieces of stone, of several pounds weight,
should have rested on the side of a perpendicular wall, till they were
enveloped in a stony cement, and united into one mass, is a supposition
impossible and absurd. It should be considered, therefore, as a thing
demonstrated, that this pudding-stone was formed in a horizontal
position, or one nearly such, and elevated after its induration. We
know not," he continues, "the force by which this elevation has been
effected; but it is an important step among the prodigious number of
vertical beds that are to be met with in the Alps, to have found some
that must certainly have been formed in a horizontal situation."[14]
[Footnote 14: Voyages aux Alpes, tom. ii § 690.]
41. Nothing can be more sound and conclusive than this reasoning; and
had the ingenious author pursued it more systematically, it must have
led him to a theory of mountains very little different from that which
we are now endeavouring to explain. If some of the vertical strata are
proved to have been formed horizontally, there can be no reason for
not extending the same conclusion to them all, even if we had not the
support of the argument from the parallelism of the layers, which has
been already stated.
42. The highly inclined position, and the manifold inflections of the
strata, are not the only proofs of the disturbance that they have
suffered, and of the violence with which they have been forced up from
their original place. Those interruptions of their continuity which
are observed, both at the surface and under it, are evidences of the
same fact. It is plain, that if they remained now in the situation
in which they were at first deposited, they would never appear to
be suddenly broken off. No stratum would terminate abruptly; but,
however its nature and properties might change, it would constitute
an entire and continued rock, at least where the effects of waste and
_detritus_ had not produced a separation. This, however, is very far
from being the actual condition of stratified bodies. Those that are
much inclined, or that make considerable angles with the horizontal
plane, must terminate abruptly where they come up to the surface. Their
doing so is a necessary consequence of their position, and furnishes no
argument, it may be said, for their having been disturbed, different
from that which has been already deduced from their inclination. There
are, however, instances of a breach of continuity in the strata, under
the surface, that afford a proof of the violence with which they have
been displaced, different from any hitherto mentioned. Of this nature
are the _slips_ or _shifts_, that so often perplex the miner in his
subterraneous journey, and which change at once all those lines and
bearings that had hitherto directed his course. When his mine reaches
a certain plane, which is sometimes perpendicular, sometimes oblique
to the horizon, he finds the beds of rock broken asunder, those on
the one side of the plane having changed their place, by sliding in
a particular direction along the face of the others. In this motion
they have sometimes preserved their parallelism, that is, the strata
on one side of the _slip_ continue parallel to those on the other; in
other cases, the strata on each side become inclined to one another,
though their identity is still to be recognized by their possessing
the same thickness, and the same internal characters. These _shifts_
are often of great extent, and must be measured by the quantity of
the rock moved, taken in conjunction with the distance to which it
has been carried. In some instances, a vein is formed at the plane of
the shift or slip, filled with materials of the kinds which will be
hereafter mentioned; in other instances, the opposite sides of the rock
remain contiguous, or have the interval between them filled with soft
and unconsolidated earth. All these are the undeniable effects of some
great convulsion, which has shaken the very foundations of the earth;
but which, far from being a disorder in nature, is part of a regular
system, essential to the constitution and economy of the globe.
The production of the appearances now described, belongs, without
doubt, to different periods of time; and, where slips intersect one
another, we can often distinguish the less from the more ancient They
are all, however, of a date posterior to that at which the waving and
undulated forms of the strata were acquired, as they do not carry with
them any marks of the softness of the rock, but many of its complete
induration.
The same phenomenon which is thus exemplified on a great scale in
the bowels of the earth, is often most beautifully exhibited in
single specimens of stone, and is accompanied with this remarkable
circumstance, that the _integrity_ of the stone is not destroyed by the
shifts, whatever wounds had been made in it being healed, and the parts
firmly reunited to one another.[15]
[Footnote 15: NOTE XI.]
43. Though such marks of violence as have been now enumerated are
common in some degree to all the strata, they abound most among the
primary, and point out these as the part of our globe which has been
exposed to the greatest vicissitudes. At their junction with the
secondary, or where they emerge, as it were, from under the latter,
phenomena occur, which mark some of those vicissitudes with astonishing
precision; phenomena of which the nature was first accurately explored,
and the consequences fully deduced, by the geologist whose system I am
endeavouring to explain. He observed, in several instances, that where
the primary schistus rises in beds almost vertical, it is covered by
horizontal layers of secondary sandstone, which last are penetrated by
the irregular tops of the schistus, and also involve fragments of that
rock, some angular, others round and smooth, as if worn by attrition.
From this he concluded, that the primary strata, after being formed at
the bottom of the sea, in planes nearly horizontal, were raised, so as
to become almost vertical, while they were yet covered by the ocean,
and before the secondary strata had begun to be deposited on them. He
also argued, that, as the fragments of the primary rock, included in
the secondary, are many of them rounded and worn, the deposition of
the latter must have been separated from the elevation of the former
by such an interval of time, as gave room for the action of waste and
decay, allowing those fragments first to be detached, and afterwards
wrought into a round figure.[16]
[Footnote 16: NOTE XII.]
44. Indeed, the interposition of a breccia between the primary and
secondary strata, in which the fragments, whether round or angular,
are always of the primary rock, is a fact so general, and the quantity
of this breccia is often so great, that it leads to a conclusion more
paradoxical than any of the preceding, but from which, nevertheless,
it seems very difficult to withhold assent. Round gravel, when in
great abundance, agreeably to a remark already made, must necessarily
be considered as a production peculiar to the beds of rivers, or
the shores of continents, and as hardly ever formed at great depths
under the surface of the sea. It should seem, then, that the primary
schistus, after attaining its erect position, had been raised up to
the surface, where this gravel was formed; and from thence had been
let down again to the depths of the ocean, where the secondary strata
were deposited on it. Such alternate elevations and depressions of the
bottom of the sea, however extraordinary they may seem, will appear to
make a part of the system of the mineral kingdom, from other phenomena
hereafter to be described.
45. On the whole, therefore, by comparing the actual position of the
strata, their erectness, their curvature, the interruptions of their
continuity, and the transverse stratification of the secondary in
respect of the primary, with the regular and level situation which
the same strata must have originally possessed, we have a complete
demonstration of their having been disturbed, torn asunder, and moved
angularly, by a force that has, in general, been directed from below
upwards. In establishing this conclusion, we have reasoned more from
the facts which relate to the _angular elevation_ of the strata,
than from those which relate to their _absolute elevation_, or their
translation to a greater distance from the centre of the earth. This
has been done, because the appearances, which respect the absolute
lifting up of the strata are more ambiguous than those, which respect
the change of their angular position. The former might be accounted
for, could they be separated from the latter, in two ways, viz. either
by the retreat of the sea, or the raising up of the land; but the
latter can be explained only in one way, and force us of necessity to
acknowledge the existence of an expanding power, which has acted on the
strata with incredible energy, and has been directed from the centre
toward the circumference.
46. When we are assured of the existence of such a power as this in the
mineral regions, we should argue with singular inconsistency, if we did
not ascribe to it all the other appearances of motion in those regions,
which it is adequate to produce. If nature in her subterraneous abodes
is provided with a force that could burst asunder the massy pavement
of the globe, and place the fragments upright upon their edges, could
she not, by the same effort, raise them from the greatest depths of the
sea, to the highest elevation of the land? The cause that is adequate
to one of these effects is adequate to them both together; for it is a
principle well known in mechanical philosophy, that the force which
produces a parallel motion, may, according to the way in which it is
applied, produce also an angular motion, without any diminution of the
former effect. It would, therefore, be extremely unphilosophical to
suppose, that any other cause has changed the relative level of the
strata, and the surface of the sea, than that which has, in so many
cases, raised the strata from a horizontal to a highly inclined, or
even vertical situation: it would be to introduce the action of more
causes than the phenomena require, and to forget, that nature, whose
operations we are endeavouring to trace, combines the possession of
infinite resources with the most economical application of them.
47. From all, therefore, that relates to the position of the strata, I
think I am justified in affirming, that their disturbance and removal
from the place of their original formation, by a force directed
from below upwards, is a fact in the natural history of the earth,
as perfectly ascertained as any thing which is not the subject of
immediate observation. As to the power by which this great effect has
been produced, we cannot expect to decide with equal evidence, but must
be contented to pass from what is certain to what is probable. We may,
then, remark, that of the forces in nature to which our experience
does in any degree extend, none seems so capable of the effect we
would ascribe to it, as the expansive power of heat; a power to which
no limits can be set, and one, which, on grounds quite independent of
the elevation of the strata, has been already concluded to act with
great energy in the subterraneous regions. We have, indeed, no other
alternative, but either to adopt this explanation, or to ascribe the
facts in question to some secret and unknown cause, though we are
ignorant of its nature, and have no evidence of its existence.
We are therefore to suppose, that the power of the same subterraneous
heat, which consolidated and mineralized the strata at the bottom of
the sea, has since raised them up to the height at which they are now
placed, and has given them the various inclinations to the horizon
which they are found actually to possess.
48. The probability of this hypothesis will appear greatly increased,
when it is considered, that, besides those now enumerated, there are
other indications of movement among the bodies of the mineral kingdom,
where effects of heat more characteristic than simple expansion are
clearly to be discovered. Thus, on examining the marks of disorder
and movement which are found among the strata, it cannot fail to be
observed, that notwithstanding the fracture and dislocation, of which
they afford so many examples, there are few empty spaces to be met
with among them, as far as our observation extends. The breaches and
separations are numerous, and distinct; but they are, for the most
part, completely filled up with minerals of a kind quite different
from the rock on each side of them, and remarkable for containing
no vestiges of stratification. We are thus led to consider the
unstratified minerals, the second of the divisions into which the whole
mineral kingdom, viewed geologically, ought to be distinguished. These
minerals are immediately connected with the disturbance of the strata,
and appear, in many instances, to have been the instruments of their
elevation.