The formation of mountains (979-983).
Mountains are made by the currents of rivers.
Mountains are destroyed by the currents of rivers.
[Footnote: Compare 789.]
That the Northern bases of some Alps are not yet petrified. And this is plainly to be seen where the rivers, which cut through them, flow towards the North; where they cut through the strata in the living stone in the higher parts of the mountains; and, where they join the plains, these strata are all of potter’s clay; as is to be seen in the valley of Lamona where the river Lamona, as it issues from the Appenines, does these things on its banks.
That the rivers have all cut and divided the mountains of the great Alps one from the other. This is visible in the order of the stratified rocks, because from the summits of the banks, down to the river the correspondence of the strata in the rocks is visible on either side of the river. That the stratified stones of the mountains are all layers of clay, deposited one above the other by the various floods of the rivers. That the different size of the strata is caused by the difference in the floods—that is to say greater or lesser floods.
The summits of mountains for a long time rise constantly.
The opposite sides of the mountains always approach each other below; the depths of the valleys which are above the sphere of the waters are in the course of time constantly getting nearer to the centre of the world.
In an equal period, the valleys sink much more than the mountains rise.
The bases of the mountains always come closer together.
In proportion as the valleys become deeper, the more quickly are their sides worn away.
In every concavity at the summit of the mountains we shall always find the divisions of the strata in the rocks.