THE SEA AT WORK.
STREAM EROSION.
“More silent, but not less efficacious, has been the action of the great rivers, as the Ganges and the Mississippi, whose waters are so heavily laden with solid particles in suspension. Each of these small particles, which trouble the limpidity of their liquid carrier, is a fragment torn from the shores washed by these rivers. Slowly but surely their currents bear to the great reservoir of the sea every atom lost to the soil, and the bars which form their deltas are as nothing compared with what the sea receives and hides away in its abysses. How can any reflecting person, observing this action, and knowing that it has been going on for many centuries, escape the conclusion that the rivers, like the ocean, are indeed preparing the final ruin of the habitable world?
“Geology confirms this conclusion in every particular. It shows us that the surface of the soil is being constantly altered over entire continents by variations of temperature, by alterations of drought and humidity, of freezing and thawing, as also by the incessant action of worms and of plants. Hence, a continuous process of dissolution, leading even to the disintegration of the most compact rocks, reducing them to fragments small enough to yield at last to the attraction of gravity, especially when this is aided by running water. Thus they travel, first down the slopes and along the torrent beds, where their angles are worn away and they become little by little transformed into gravel, sand and ooze; then in the rivers which are still able, especially at flood-times, to carry away this broken up material, and to bear it nearer and nearer to their outlets.
“It is easy to predict what must necessarily be the final result of this action. Gravity, always acting, will not be satisfied until every particle subject to its law has attained the most stable position conceivable. Now, such will be the case only when matter is in the lowest position possible. Every surface, must therefore disappear, except the surface of the ocean, which is the goal of every agency of motion; and the material borne away from the crumbling continents must in the end be spread over the bottom of the sea. In brief, the final outcome will be the complete levelling of the land, or, more exactly, the disappearance of every prominence from the surface of the earth.
AT FLOOD-TIME.
“In the first place, we readily see that near the river mouths the final form of the dry land will be that of nearly horizontal plains. The effect of the erosion produced by running water will be the formation on the water-sheds of a series of sharp ridges, succeeded by almost absolutely horizontal plains, between which no final difference in height greater than fifty meters can exist.
“But in no case can these sharp ridges, which, on this hypothesis, will separate the basins, continue long; for gravity and the action of the wind, filtration and change of temperature, will soon obliterate them. It is thus legitimate to conclude that the end of this erosion of the continents will be their reduction to an absolute level, a level differing but little from that at the river outlets.”