the dawn of civilization, and through the historic ages, down to the present time: his speculations, therefore, comprise but a comparatively brief period—the few thousand years that have elapsed since the creation of man and the animals which are his contemporaries. The geologist, on the other hand, directs his views to the character and causes of the changes, that have taken place throughout the organic and inorganic kingdoms of nature; from the period when "the earth was without form and void," through the innumerable ages chronicled by the relics of the races of animals and plants which have successively appeared, and flourished awhile, and become extinct: his investigations also embrace the consideration of the physical revolutions which have swept over the earth's surface during the human epoch, and of those that are still in progress.
In the ancient sedimentary rocks, the remains of the animals and plants which inhabited the land, the rivers, and the seas, when those strata were deposited, occur in such abundance and variety, that the naturalist can readily determine the characters of the terrestrial and marine faunas and floras which prevailed in those remote eras. The elementary principles of geology are now so generally disseminated, that I take it for granted every intelligent person is aware that all the rocks and strata composing the dry land were originally in a softened or fluid state, either from the effects of water or from exposure to a high temperature;—that the strata are accumulations of mud, sand, or other detritus, the sedimentary deposits of streams, rivers, and seas, combined with the durable remains of animals and plants which lived either on the land or in the water;—that these beds of organic and inorganic materials have been consolidated by chemical and mechanical agency, and subsequently been elevated from beneath the waters, at various periods, by those physical forces which are constantly in action in the profound depths of the earth, and of which the earthquake and the volcano are the paroxysmal effects;—and that such transmutations of the sea and of the land are perpetually taking place.
Throughout the entire series of the secondary and tertiary formations, though the most recent of the latter contain relics of species now existing, no traces of the human race have been discovered. It is only in the deltas, estuaries,
