A somewhat curious calculation has been made, to illustrate the
different modes of working of these two mighty powers--Fire and Water.

The amount of land swept away each year in mud, and borne to the ocean
by the River Ganges, was roughly reckoned, and also the amount of land
believed to have been upheaved several feet in the great Chilian
earthquake.

It was found that the river, steadily working month by month, would
require some four hundred years to carry to the sea the same weight of
material, which in one tremendous effort was upheaved by the fiery
underground forces.

Yet we must not carry this distinction too far. Fire does not always
work suddenly, or water slowly; witness the slow rising and sinking of
land in parts of the earth, continuing through centuries; and witness
also the effects of great floods and storms.

The crust of the earth is made of rock. But what is rock made of?

Certain leading divisions of rocks have been already considered:

The Water-made Rocks;

The Fire-made Rocks, both Plutonic and Volcanic;

The Water-and-Fire-made Rocks.

The first of these--Water-made Rocks--may be subdivided into three
classes. These are,--