so as to form islands.]
Whirlpools.
975.
Whirlpools, that is to say caverns; that is to say places left by precipitated waters.
On the alterations in the channels of rivers.
976.
OF THE VIBRATION OF THE EARTH.
The subterranean channels of waters, like those which exist between the air and the earth, are those which unceasingly wear away and deepen the beds of their currents.
The origin of the sand in rivers (977. 978).
977.
A river that flows from mountains deposits a great quantity of large stones in its bed, which still have some of their angles and sides, and in the course of its flow it carries down smaller stones with the angles more worn; that is to say the large stones become smaller. And farther on it deposits coarse gravel and then smaller, and as it proceeds this becomes coarse sand and