Thus, then, to whatever portion of the earth's surface we turn our eyes, we find the proofs of igneous action; our existing volcanoes, protruding themselves through the newer stratified formations, and even the diluvium, being in some cases more recent in their origin than the last great catastrophe to which the earth has been subjected; those of more ancient date forcing their way through the upper and lower secondary and transition formations, which are also cut and intersected by dykes of trap, while granite from the size of mountain masses down to their veins, has upheaved and penetrated the oldest stratified rocks. We also find great extents of country rising, sometimes gradually, sometimes suddenly, above their former level.
Mountains, then, are not the nucleus on which our continents and islands have been deposited, but are of subsequent origin, and have in their rise elevated the land to such a height as to be no longer accessible to the waters of the ocean. We may, even by examining through what strata the mountains have been raised, or those which compose their sides and crests when the elevating agent has not pierced through to the surface, infer the geological age which gave them birth. A research of this sort has been recently attempted and conducted with great ability by M. E. De Beaumont.
We shall quote an abstract of his reasoning from the "Annuaire," for 1830, in the words of Arago, which will also serve to illustrate various other points upon which we have touched.
"Among the formations of so many different kinds that form the crust of our globe, there is a class which has been called sedimentary (terrains de sediment). Those formations to which this name is properly applied, are composed wholly, or in part, of detritus, carried by water like the mud of our rivers, or the sands of the beaches of the sea. These sands, in a state of greater or less division, and agglutinated by siliceous or calcareous cements, form the rocks called sandstones.
"Certain calcareous formations may also be reckoned in the same class, even when they are wholly soluble, as is however rare, in nitric acid; for the fragments of shells which they contain, show, in another and perhaps better manner, that their formation has also taken place in the bosom of the waters.
"Sedimentary formations are always composed of successive layers, that are very distinctly marked. The more recent of them may be arranged into four great divisions, which, in the order of their antiquity, are
"The oolitic series or limestone of Jura;
"The system of greensand and chalk;
"The tertiary series; and finally
"The diluvian deposits.