By the study of the successive beds, more especially of those deposited in the times of continental submergence, we obtain a table of geological chronology which expresses the several stages of the formation of the earth's crust, from that early time when a solid shell first formed on our nascent planet to the present day. By collecting the fossil remains embedded in the several layers and placing these in chronological order, we obtain in like manner histories of animal and plant life parallel to the physical changes indicated by the beds themselves. The facts as to the sequence we obtain from the study of exposures in cliffs, cuttings, quarries, and mines; and by correlating these local sections in a great number of places, we obtain our general table of succession; though it is to be observed that in some single exposures or series of exposures, like those in the great canons of Colorado, or on the coasts of Great Britain, we can often in one locality see nearly the whole sequence of beds. Let us observe here also that, though we can trace these series of deposits over the whole of the surfaces of the continents, yet if the series could be seen in one spot, say in one shaft sunk through the whole thickness of the earth's crust, this would be sufficient for our purpose, so far as the history of life is concerned. The evidence is similar to that obtained by Schliemann on the site of Troy, where, in digging through successive layers of _débris_, he found the objects deposited by successive occupants of the site, from the time of the Roman Empire back to the earliest tribes, whose flint weapons and the ashes of their fires rest on the original surface of the ground. Let us now tabulate the whole geological succession with the history of animals and plants associated with it: ANIMALS. SYSTEMS OF FORMATIONS. PLANTS. Age of Man and Mammalia. Kainozoic. { Modern, { Pleistocene, Angiosperms and { Pliocene, Palms dominant. { Miocene, { Eocene. Age of Reptiles. Mesozoic. { Cretaceous, Cycads and Pines { Jurassic, dominant. { Triassic. Age of Amphibians and Fishes. Age of Invertebrates. Palæozoic. { Permian, Acrogens and { Carboniferous, Gymnosperms { Erian, dominant. { Silurian, { Ordovician, { Cambrian, { Huronian (Upper). Age of Protozoa. Eozoic. { Huronian (Lower), Protogens and Algæ. { Upper Laurentian, { Middle Laurentian, { Lower Laurentian.