And part of the soil is called to wash away
In storms and streams shave close and gnaw the rocks.
Besides, whatever the earth feeds and grows
Is restored to earth. And since she surely is
The womb of all things and their common grave,
Earth must dwindle, you see and take on growth again.

Etna presents us not merely with an image of the power of subterranean heat, but a record also of the vast period of time during which that power has been exerted. A majestic mountain has been produced by volcanic action, yet the time of which the volcanic forms the register, however vast, is found by the geologist to be of inconsiderable amount, even in the modem annals of the earth's history. In like manner, the Falls of Niagara teach us not merely to appreciate the power of moving water, but furnish us at the same time with data for estimating the enormous lapse of ages during which that force has operated. A deep and long ravine has been excavated, and the river has required ages to accomplish the task, yet the same region affords evidence that the sum of these ages is as nothing, and as the work of yesterday, when compared to the antecedent periods, of which there are monuments in the same district.

I shall conclude, for the time being, by saying that until Philosophers make observations (especially of mountains) that are longer, more attentive, orderly, and interconnected, and while they fail to recognize the two great agents, fire and water, in their distinct affects, they will not be able to understand the causes of the great natural variety in the disposition, structure, and other matter that can be observed in the terrestrial globe in a manner that truly corresponds to the facts and to the phenomena of Nature.

One naturally asks, what was the use of this great engine set at work ages ago to grind, furrow, and knead over, as it were, the surface of the earth? We have our answer in the fertile soil which spreads over the temperate regions of the globe. The glacier was God's great plough.

When the aggregate amount of solid matter transported by rivers in a given number of centuries from a large continent, shall be reduced to arithmetical computation, the result will appear most astonishing to those...not in the habit of reflecting how many of the mightiest of operations in nature are effected insensibly, without noise or disorder.

While a glacier is moving, it rubs and wears down the bottom on which it moves, scrapes its surface (now smooth), triturates the broken-off material that is found between the ice and the rock, pulverizes or reduces it to a clayey paste, rounds angular blocks that resist its pressure, and polishes those having a larger surface. At the surface of the glacier, other processes occur. Fragments of rocks that are broken-off from the neighbouring walls and fall on the ice, remain there or can be transported to the sides; they advance in this way on the top of the glacier, without moving or rubbing against each other … and arrive at the extremity of the glacier with their angles, sharp edges, and their uneven surfaces intact.

With the sole guidance of our practical knowledge of those physical agents which we see actually used in the continuous workings of nature, and of our knowledge of the respective effects induced by the same workings, we can with reasonable basis surmise what the forces were which acted even in the remotest times.