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.