In examining the tops of granite mountains, or where this rock is exposed to the weather, we may perceive those two species of decay proceeding together. The external surface of the stone, where there is a sufficient mixture of feltspar, is separating into grains which form a species of sand, being nothing but the particles of granite separating by means of the decaying sparry part. But a similar progress may be observed, from the external surface penetrating in lines the mass of solid rock, and dividing that mass into the rectangular blocks into which those exposed places are gradually resolved.
Now the tops of all those mountains are formed into an assemblage of pyramids, declining in height from the central pyramid; and all those pyramids are again in like manner subdivided into lesser pyramids. But the smallest of those pyramids are no other than the rectangular blocks into which those granite masses always separate by the influence of the atmosphere.
It will now be evident, that those mountains, thus resolving into separate blocks, must acquire this series of pyramidal constructions; for, in every particular mass of mountain, there must be a central part, from which the separated blocks cannot be removed, while those around, or towards the sides, are detached by the swelling water upon freezing, and separated from the more central masses which are thus the latest of being removed.
It is impossible to see this series of pyramidal relics, without at the same time perceiving that manner of formation, by the gradual resolution of the solid mass of granite, as it comes to be exposed in succession to the influences of the atmosphere, which M. de Saussure has termed les ravage du temps.
But if it be in this manner, that time wastes the solid masses of this globe; and if all the solid masses of the earth have acquired their solid state by the same means, i.e. by heat and fusion, as is maintained in the present theory, we should find similar pyramidal mountains formed of different materials. Now there can be nothing more different than masses of lime-stone and those of granite. But pyramidal mountains are equally formed of those two different materials. In plate V, under the letter B, may be seen the calcareous pyramids which are near the col de la Seigne, and which in plate VI. are represented under the letter G.
Here is a view of the summit of the Alps, from whence we may be allowed to draw the most important conclusions in favour of our theory.
This summit is of solid granite, a mass in which there is no stratification, such as is to be perceived in all the other masses of those alpine regions. With regard again to the extent of this mass of granite, its basis is about two leagues in breadth, by at least thrice that space in length; and now we are to consider in what shape this mass of granite presents itself to our view.
The summit of Mont Blanc, which may be considered as in the centre of this mass, is a pyramid; and this great central pyramid is surrounded by a number of other great pyramids of the same kind. The points of those pyramids are extremely lofty; and, having sides often vastly steep, if not perpendicular, those colossal pyramids rise from the icy valleys in such a shape as has given occasion to their being named needles. Thus we find the whole space of this granite mass consisting of a mixture of icy valleys, and pyramidal rocks on which hardly any thing rests.
Now, these lofty rocks or pointed mountains must have been either originally formed of that shape, or posteriorly hewn out by the hand of nature, gradually wasting mountains in the course of time, and operations of the surface. If it is by the first that we are to explain the present state of things, then observation is superfluous, and our reasoning is at an end; for, when even observation should not contradict the proposition, which it actually does, it would be useless, as it can afford no data from a former state, which is supposed to have been no other than it is at present; and reasoning cannot be admitted if we have no data. Therefore, if we are to reason upon the subject, we are obliged to admit, that nature must have hollowed out of the solid rock all those pyramidal mountains, and a system of inclined valleys carrying the ice from the summits.
Let us now reason from our principles, in order to see how far the present appearances of things would naturally result from those wasting causes acting upon a mass of granite, of a given basis and of sufficient height, during a space of time which is unlimited.