Illustrations of the Huttonian Theory of the Earth

by John Playfair

Note v. § 10.

Transportation of the materials of the strata.

156. The great transportation or travelling of the materials of the strata, supposed by Dr Hutton, has been treated as absurd by some of his opponents, particularly De Luc and Kirwan. These philosophers seem not to have observed, that their own system, and indeed every system which derives the secondary strata from the primary, involves a transportation of materials, hardly less than is supposed in the Huttonian theory, and a degradation of the primeval mountains, in many instances much greater. To form some notion of this degradation, it must be recollected, that the primeval mountains, which furnished the materials of the secondary strata in the plains, cannot have stood in the place now occupied by these plains. This is obvious; and therefore we must necessarily regard the secondary strata as derived from the primitive mountains which are the nearest to them, and of which a part still remains. This part is sufficient to define the base of the original mountains; and the quantity of the secondary strata which surround them may help us to make some estimate of their height. Let us take, for instance, the extensive tract of secondary country about Newcastle, where coal mines have been sunk through a succession of secondary strata, to the depth of more than a thousand feet. This secondary country may be considered as comprehending almost the whole of the counties of Northumberland and Durham, and probably as extending very far under the part of the German Ocean which washes their coasts; and the whole strata composing it must be derived, on the hypothesis we are now considering, from the Cheviot Hills, on one side, and from those in the high parts of Westmoreland and Cumberland on the other, comprehending the Alston-Moor Hills, and the large group of primary mountains, so well known from the sublime and romantic scenery of the Lakes. Now, the mountains which stood on this base, had not only to supply the materials for the tract already mentioned, on the east, but had also their contingent to furnish to the plains on the west and north; the Cheviots to Roxburghshire and Berwickshire; the Northumberland mountains to the coal strata about Whitehaven, and along the sea coast to Lancashire. On the whole, we shall not exceed the truth, if we suppose, that the secondary strata, at the feet of the above mountains, are six or seven times more extensive than the base of the mountainous tract. If then we take the medium depth of these secondary strata to be one thousand feet, it is evident, that the mass of stone which composes them, if it were placed on the same base with the primitive mountains, would reach to the height of six thousand feet. This is supposing the mass to preserve the breadth of its base uniformly to the summit; but if it be supposed to taper, as mountains usually do, we must multiply this six thousand by three, in order to have the height of these primeval mountains, which, therefore, were originally elevated not less than eighteen thousand feet; in height, therefore, they once rivalled the Cordilleras, and are now but poorly represented by the hills of Skidaw and Helvellyn. It were easy to show, that this estimate is still below the result that strictly follows from the Neptunian hypothesis; but it is unnecessary to proceed further, than to prove, that the principle of the degradation of mountains, is involved in that hypothesis to an excessive and improbable degree; and that the supporters of it, have either been guilty of the inconsistency of refusing to Dr Hutton the moderate use of a principle, which they themselves employ in its utmost extent, or of not having sufficiently adverted to the consequences of their own system.

157. The formation of secondary strata from the degradation of the contiguous mountains, on close examination, is subject to many other difficulties of the same kind. Mountains of secondary strata, and nearly horizontal, are found in this island of the height of three thousand feet. Such are Ingleborough, Wharnside, and perhaps some others on the west of Yorkshire. The whole chain, indeed, for secondary mountains, is of great elevation. The strata are of limestone, and of a very coarse-grained sandstone, alternating with it. No mountains can more clearly point out, that the strata of which they consist were once continued quite across the vallies which now separate them; and hence, if the materials of those strata were indeed furnished from any contiguous primitive mountains, the latter must have been, out of all proportion, higher than any mountains now in Britain.

158. Thus, a great degradation of the primitive mountains, and of course a great travelling of their materials, is proved to make a necessary part of the Neptunian theory. The extent of this travelling or transportation may be rendered more evident, if we apply a similar mode of reasoning to larger portions of the globe. The north-west of Europe furnishes us an instance of a very extensive tract of secondary country, comprehending the greater part of Britain, the whole of Flanders and Holland, part of Germany, the northern provinces of France, and probably the bed of the German Ocean, at least for a great extent. Within this circle almost all is secondary, and on the sides of it all round are placed ridges or groups of primitive mountains, namely the mountains of Auvergne, at least in part, and going round by the east, the Alps, the Vosges, the Hartz, the Highlands and Western Islands of Scotland, the hilly countries of Cumberland, Wales, and Cornwall. This zone of primitive mountains, on the supposition of the Neptunists, must have risen up in the form of islands in the great ocean, that originally covered the earth, forming a kind of circular Archipelago, including in its bosom a sea, which was from seven to five hundred miles in diameter. Over the whole of this extent, the detritus of the above mountains must have been carried, in order to form the flat interjacent countries which are now exposed to our view. Such then, even on their own supposition, is the extent to which the Neptunists must admit that the materials of the primeval mountains were transported by the ocean.

159. This transportation of materials, may not be so great as that which is involved in Dr Hutton's theory, but is such as should make the enemies of his system consider, how nearly the principles they must introduce, agree with those that they would reject. This is one fact, out of many, which shows, that there is at present a much nearer agreement between the systems of geology, than between their authors.

160. To these facts, demonstrating the great transportation of fossils in some former conditions of the globe, we may add another, recognised by all mineralogists. The animal exuviæ contained in limestone and marble, are often known to belong to seas, extremely remote from the countries where they are now found. In the chalk-beds of England, in the limestones of France, a great proportion of the petrifactions belong to the tropical seas, and appear to have been brought from the vicinity of the equator. Buffon observes, that of the fossil shells found in France, it has been disputed, whether the foreign are not more numerous than the native; and, though he is himself of opinion that they are not, it is evident that they must bear a considerable proportion to the whole.[68] In the petrifactions of Monte Bolca, near Verona, where the impressions of fish are preserved between the laminæ of a calcareous schistus, one hundred and five different species have been enumerated, of which thirty-nine are from the Asiatic seas, three from the African, eighteen from those of South, and eleven from those of North America.[69] Similar observations have been made on the marine plants, and the impressions of vegetables, found in rocks, in different parts of Europe. At St Chaumont, near Lyons, is found an argillaceous schistus, covering a bed of coal, every lamina of which is marked with the impressions of the stem, leaf, or other part of some plant; and it happens, says M. Fontenelle, by an unaccountable destination of nature, that not one of these plants is a native of France. They are all ferns of different species, peculiar to the East Indies, or the warmer climates of America. Here also was found the fruit of a tree, which grows only on the coasts of Malabar and Coromandel.[70]

[68] Buffon, Théorie de la Terre, art. 8.

[69] Saussure, Voyages aux Alpes, tom. iii. § 1535.

[70] Mém. De l'Acad. Des Sciences, 1718, p. 3 and 287; and 1721, p. 89, &c.

The same holds of the bodies of amphibious animals which now make a part of the fossil kingdom. The head and the bones of crocodiles have been found in the island of Shepey, at the mouth of the Thames; and the remains of an animal of the same species, but of a variety now peculiar to the Ganges, have been discovered in the alum rocks on the coast of Yorkshire.[71] These proofs of the transportation of materials by the sea, have the advantage of involving nothing hypothetical, and of being equally addressed to the geologists of every persuasion.

[71] Phil. Trans. vol. l. p. 688. Camper denies that the remains here mentioned belong to the crocodile, or any amphibious animal, and refers them to the balænaæ. He passes the same judgment on those fossil bones from St Peter's Mount, near Maestricht, which have been supposed to belong to the crocodile; he looks on them as belonging to whales, though of an unknown species. In this Mount, so famous for its petrifactions, he finds many specimens of bones, which he thinks belong to the turtle. Phil. Trans. vol lxxvi. p. 443. The opinion of an author, so well skilled in comparative anatomy, must be regarded as of great weight: if it takes from our argument in one part, it adds to it in another, and the acquisition of the turtle makes up abundantly for the loss of the crocodile.

On this subject I cannot help observing, that the accurate comparison of the animal exuviæ of the mineral kingdom, with their living archetypes, is not merely a curious inquiry, but is one that may lead to important consequences, concerning the nature and direction of the forces which have changed, and are continually changing, the surface of the earth.

161. These remarks I have thought it proper to add to the proofs of the composition of the present from former strata, in order to show, that the great transportation of materials involved in that supposition, is not only conformable to the hypothesis of the Neptunists concerning the secondary strata, but is also proved by the most direct evidence, independently of all hypothesis. All this reasoning regards the ancient state of the globe. Whether such a travelling of stony bodies makes a part of the system now actually carrying on, will be considered in another place.[72]

[72] See Note xix.