The cKvision of the crust of the earth into three great orders or epochs of time, in which a peculiar class of rock was formed or deposited, is a natural as well as proper distinction. The primary, secondary and tertiary rocks are distinguished from each other, not so much by the physical characteristics of the stone composing them as by the genus and species, and, in some cases, the totally different forms of life which inhabited the world at the time of the deposition of these rocks. These relics of past life—these monuments of extinct existence, found by the mason in the stone and by the child in the pebble of the brook, looking sometimes like a shell carved in stone, or a footmark that has suddenly become petrified—these relics are called "fossils;" the process by which they have been formed is very simple, and is going on.all around us at the present day. Those animals and insects of whose outer form we have such perfect imprints, those leaves and branches that are now found in the coal fields of our country, once lived, as do the animals of the passing hour, and the ferns and mosses of familiar glens. They died; and the shell left upon the sea-shore became gradually covered with mud, the mud hardened, the bed of the ocean was gradually upheaved, and the shell remained encased in its hard tomb. The home of the fern and moss, gigantic as cedars and spreading out like vines, became a swamp, was inundated with water, the mud rose, a process of carbonization was gradually, but surely and minutely carried on; and we now discover their shapes and forms in the coal that gives us warmth and light, and by the destruction of which we create a gas which will effect the same purpose as was effected when the coal was made. Fossilization is going on now as surely as ever before ; and though historians may prejudice our age, and novelists wrap around it a mantle of romance, yet the forms of life which now exist will tell a tale to future generations—a tale cut by Nature's hand in her own monumental marbles, and so full of truth that none can gainsay it. Civilization leaves her mark even on the shape and size of animals; her magic touch will be retained long afterthe recipients have sunk into oblivion.