Granite and whinstone, or basaltes, though distinct compositions, thus graduating into each other; and whinstone, as well as porphyry, being without doubt a species of lava, we may consider the granite which is found in mass without stratification, in like manner as we do the masses of whinstone, basaltes, or Swedish trap, as having flowed in the bowels of the earth, and thus been produced by the chance of place, without any proper form of its own, or in an irregular shape and construction. In this manner would be explained the irregular shape or structure of those granite masses; and thus great light would be thrown upon the waved structure of the stratified alpine stone, which, though it has not been made to flow, has been brought to a great degree of softness, so as to have the original straight lines of its stratification changed to those undulated or waving lines which are in some cases extremely much incurvated.
It remains only to confirm this reasoning, upon our principles, by bringing actual observation to its support; and this we shall do from two of the best authorities. The Chevalier de Dolomieu, in describing the volcanic productions of Etna, mentions a lava which had flowed from that mountain, and which may be considered as a granite. But M. de Saussure has put this matter out of doubt by describing most accurately what he had seen both in the Alps and at the city of Lyons. These are veins of granite which have flowed from the contiguous mass into the stratified stone, and leave no doubt with regard to this proposition, that the granite had flowed in form of subterranean lava, although M. de Saussure has drawn a very different conclusion from this appearance. I have also a specimen from this country of a vein of granite in a granite stone, the vein being of a smaller grain than that of the rock which it traverses.[20]
Footnote 20:[ (return) ] This is what I had wrote upon, the subject of granite, before I had acquired such ample testimony from my own observations upon that species of rock. I have given some notice, in the 3d vol. of the Transactions of the Edinburgh R.S. concerning the general result of those observations, which will be given particularly in the course of this work.
It will thus appear, that the doctrine which of late has prevailed, of primitive mountains, or something which should be considered as original in the construction of this earth, must be given up as a false view of nature, which has formed the granite upon the same principle with that of any other consolidated stratum; so far as the collection of different materials, and the subsequent fusion of the compound mass, are necessary operations in the preparation of all the solid masses of the earth. Whatever operations of the globe, therefore, may be concluded from the composition of granite masses, as well as of the alpine strata, these must be considered as giving us information with regard to the natural history of this earth; and they will be considered as important, in proportion as they disclose to us truths, which from other strata might not be so evident, or at all made known.
Let us now examine the arguments, which, may be employed in favour of that supposition of primitive mountains.
The observations, on which naturalists have founded that opinion of originality in some of the component parts of our earth, are these; first, They observe certain great masses of granite in which stratification is not to be perceived; this then they say is an original mass, and it is not to be derived from any natural operation of the globe; secondly, They observe considerable tracts of the earth composed of matter in the order of stratification as to its general composition, but not as to its particular position, the vertical position here prevailing, instead of the horizontal which is proper to strata formed in water; this, therefore, they also term primitive, and suppose it to be from another origin than that of the subsidence of materials moved in the waters of the globe; lastly, They observe both strata and masses of calcareous matter in which they cannot distinguish any marine body as is usual in other strata of the same substance; and these calcareous masses being generally connected with their primitive mountains, they have also included these collections of calcareous matter, in which marine bodies are not observed, among the primitive parts which they suppose to be the original construction of this globe.
It may be proper to see the description of a calcareous alpine mountain. M. de Saussure gives us the following observations concerning a mountain of this kind in the middle of the Alps, where the water divides in running different ways towards the sea. It is in describing the passage of the Bon-Homme, (Tom. 2. V. dans les Alpes).
"§ 759. Sur la droite ou au couchant de ces rochers, on voit une montagne calcaire étonnante dans ce genre par la hardiesse avec laquelle elle élève contre le ciel ses cimes aigues et tranchantes, taillées à angles vifs dans le costume des hautes cimes de granit. Elle est pourtant bien sûrement calcaire, je l'ai observée de près, et on rencontre sur cette route les blocs qui s'en détachent.
"Cette pierre porte les caractères des calcaires les plus anciennes; sa couleur est grise, son grain assez fin, on n'y apperçoit aucun vestige de corps organisés; ses couches sont peu épaisses, ondées et coupées fréquemment par des fentes parallèles entr'elles et perpendiculaires à leurs plans. On trouve aussi parmi ces fragmens des brèches calcaires grises."
Here is a mountain which will rank with the most primitive of the earth; But why? only because it is extremely consolidated without any mark of organised body. Had there been in this mountain but one single shell, we should not then have scrupled to conclude that the origin of this lofty mountain had been the same with every marble or limestone in the earth. But though, from the structure of this stone, there is no mark of its having been formed immediately of the calcareous parts of animals, there is every mark of those calcareous strata having been formed like other marbles by deposit in the waters of the globe.