Imatges de pàgina
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SUMMARY VIEW

§1. GEOLOGY the most extensive and the most complex of

sciences. 2. The too hasty assignment of causes to past effects

has produced various contradictory Theories of the Earth.

3. The history of the Earth inseparably connected with that of

Man. 4. Geology a science useless to mankind, till brought

forward in the systems of modern philosophers; the history of

the earth and of the human race having been sufficiently made

known by the Mosaic records, and by Pagan traditions derived

from a similar source. 5. All information essential to men on

this subject had thus been afforded them by Revelation. 6. But

Geology having been represented by some authors as in opposi-

tion to the history of Moses, the study of this science is on that

account become essential to Divines. 7. The duties and thé

destination of men involved in a question which concerns their

origin. 8. The first geological systems contrary to Genesis have

fallen to the ground. 9. Those in defence of Genesis equally

premature. 10. Importance of establishing some fundamental

points in Geology. 11. Mr. Playfair's Illustrations of the Hut--

tonian Theory one of the latest and most methodical works on

this science. 12. Dr. Hutton had formed a general system from

some mineralogical details. 13. Mr. Playfair's statement of the

great extent of knowledge required in geology. 14. Ill conse-

quences of scepticism in this science. 15. General motives ad-

duced with reason by Mr. Playfair for hoping that truth in

geology may be attained; but its attainment would be pro-

tracted by the means which he points out. 16. He believes

that Dr. Hutton's theory has been little noticed, not on account

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of ts nature, but of its obscurity: he is however mistaken, for it is easily understood. 17. Cause of the neglect of Bacon among superficial naturalists. 18. Bacon's design was not to erect the edifice of science, but only to lay its foundation on fixed principles. 19. The deficiency of his materials. 20. His opinion that facts ought to be exclusively the objects of attention. 21. All geological questions must be resolved by facts. 22. The theory, distinctively called Huttonian, connected with hypotheses common to many other theories. 23. Dr. Hutton and Mr. Playfair consider the alternate changes supposed in their theory, and the final causes which they assign to these changes, as reciprocally proving cach other. 24. Outline of the Huttonian theory. 25. No limit assignable to the number of alternate changes supposed in it, from sea to land, and from land to sea; whence all knowledge of a primitive state of the earth is placed beyond our reach. 26. Aspect under which Mr. Playfair presents his hypotheses. 26. a. The fear of incurring the imputation of weakness may induce many to acquiesce in his. theory, though they may not comprehend the ground of his confidence. 27. No other system could lead to the discussion of so many important geological questions. 28. The origin of the mineral strata one of the greatest objects of this science. 29. Huttonian opinions respecting the degradation of our continents, and the action of external causes upon them. 30. Respecting the sediments of rivers, and the materials detached by the sea from its coasts. 31. Whether our mineral strata could have been formed from the detritus of former continents. 31. a. Cause assigned by Dr. Hutton for the consolidation of loose materials. 32. The birth of our continents produced by some great revolution upon our globe. 33. Ruinous appearance of the mineral strata. 34. Either their mass must have been raised, or the level of the sea must have sunk. 35. Importance of ascertaining the antiquity of our continents. 36. Necessity of properly classing the observations made in geological travels. 37. No inquiries made in early times respecting an antecedent state of

* In the original there is an accidental repetition of the numbers of some of the sections; a similar repetition has necessarily occurred in the translation, in order that the numbers may correspond.

the

the earth. 38. Attention first attracted to this object by the marine shells found at a distance from the sea. 39. However erroneous the first theories of the earth may have been, they have yet served to accumulate materials, by which geology is now be come a solid science. 40. It is more fixed than is generally supposed. 41. The confusion which has arisen in it can be dissipated only by more attentive study. 42. Distinction to be made between phenomena produced by causes still in action, and by such as have ceased to act. 43. The production of our conti nents to be ascribed to causes which have ceased to act, and the modification of their original state to causes still in action. 44. The original state of our continents, and likewise their age, determinable by the action of actual causes. 45. Their small antiquity already proved by Mr. De Luc, in his Lettres phys. et mør. sur l'Hist. de la Terre et de l'Homme. 46. His answer to Dr. Schmieder's theory; and the difference between that and Dr. Hutton's. 47. The first point necessary to be fixed in geology is the state of our continents at their birth. 48. Great importance of M. de Saussure's observations on mountains. 49. The original and actual states of the strata composing mountains afford a clue to the knowledge of past events. 50. The Huttonian theory excludes granite, porphyry, &c. from the number of stratified substances. 51. The production of granite by chemical precipitations was the first operation of physical causes on our globe; other strata have been successively formed in the same manner: the catastrophes undergone by the whole mass of strata have produced the relative differences of level between mountains and plains. 52. Necessity of studying the effects formerly resulting from causes, which, though still existing, no longer produce such effects, on account of the change of circumstances. 53. Reference to Mr. De Luc's Lettres sur l'Hist. physique de la Terre, adressées a M, le Prof. Blumenbach. 54. Nothing originally produced under the form of mountains. 55. The principal points of Mr. De Luc's Theory: I. Respecting the origin of our continents, II. Origin of our mountains and plains. III. Islands of the ancient sea, of which some sunk beneath the level of the waters, with all their animals and vegetables; IV. While others, not submerged, became the summits of our present mountains, and the sources of vegetation for the new continents. V. Retreat of

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the sea from the new continents, to cover those ancient ones which sunk. VI. Permanence of level of the new sea. VII. Shortness of the time clapsed since the above revolution. 56. Nothing conjectural in this theory, facts being its only foundation. 57. The strata of granite form the most ancient geological monu55. Effects produced on the new continents by atmospherical causes. 59. The production of granite must have been a first operation, resulting from the accession of some new cause. 60. How far Chemistry is useful in Geology. 61. Liquidity being necessary to every chemical precipitation, the first change which took place in the mass containing the ingredients of granite consisted in its acquiring liquidity. 62. This liquidity could have been produced by the union of fire only with the molecules of the mass. 63. M. de la Métherie's misconception of this point. 64. Water, ice, and aqueous vapour, are the three forms under which that substance now appears, which, previously to its union with the fire of liquefaction, could not be described by either of those terms. 65. In that elementary state, the particles of this substance were intermixed with all others; when united with fire, it formed the primordial liquid, whence our mineral strata and the atmosphere were successively separated; and the waters of the present sea then remained as a residuum. 66. Fire being composed of light, and of another substance belonging to the atmosphere and to terrestrial bodies, the latter, though intermixed with all other elementary particles, could produce neither heat nor liquidity, till it received the addition of light. 66. a. The source of light beyond the reach of philosophical research. 67. The sea, having lost all the substances which produced our mineral strata, no such precipitations now take place in it; nor is the mass of the strata any longer subject to the catastrophes, by which their preceding revolutions had been occasioned. 68. Volcanos have not contributed to these effects in any way yet discovered. 69. The causes of the successive differences of precipitations, and of the subsequent catastrophes of the strata, must have been contained within the earth itself. 70. Question whether the highest parts of the earth have been raised, or the lowest have subsided. 71. The existence of caverns a fixed point in Geology; but, according to the theory of subsidence, they have been mostly filled 'up; according to that of elevation, they must still

exist.

exist. 72. The object of the following Dissertation will be to examine how far the original state of each part of the surface of our continents can be determined by an investigation of the causes which have acted on them, and of the effects produced by those causes.

DISSERTATION

On the geological phenomena which determine the state of our continents at their birth. Preceded by some general remarks on the causes which retard decisions in the study of Nature; and containing an examination of Dr. HUTTON's Theory of the Earth,

$73. The state of our continents at their birth forms a central point, to which all observations of phenomena ought to tend. 74, 75. Necessity of studying the causes now in action on the continents, and determining what effects they have already produced. 76. The same phenomenon, accompanied by differ ent circumstances, requires repeated observation. 77. The observation of phenomena in their various associations with cach other, will enable us to ascend to their respective causes, which are all mutually connected by corresponding links. 78. Eager ness of the human mind to generalize phenomena, before it has sufficiently ascertained their distinctive characters. 79. The decomposition of phenomena recommended by Bacon. 80. Danger of generalizing complicated phenomena. 81. No conclusions relative to causes should be drawn, until the most remote have been studied no less carefully than the immediate, and until the circumstances have been distinguished by which the phenomena, are connected with each other. 81. a. A previous assemblage of solid general principles leads to the only safe way in which conclusions may be formed. 82. Generalizations, however just, bear no intrinsic characters of truth. 83, 84. Details of phenomena are therefore required, to furnish proofs of the truth of generalizations. 85. The state of our continents at their origin can be determined only by an investigation of the causes now operating, and of the changes already produced. 86. Conclusions drawn by Dr. Hutton from this mode of inquiry. 87. Mr. De Luc had formerly addressed four letters to Dr. Hutton on the subject of his theory. 88. These were little noticed by that gentleman, and by Mr. Playfair, probably because

they

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