2. THE PROBABLE DURATION OF LIFE IN THE DIFFERENT EPOCHS. The geologist will tell us not to look at one but at the various families, of all kinds and of all habits, which his science has brought to light, and so many of whose remains he has disinterred from the earth. Every formation abounds with them. They flourished through every epoch. The epochs are many. The tribes which existed and perished in them are many. To allow time for the coming in and the going out, and the fulfillment of their various destinies, what an untold, incalculable amount of ages must have elapsed! Now, give the millions of years supposed, and the wonder some may not hesitate to confess is, that there are so few, and not so many, of the former creatures of the earth which have re-appeared in our geological catalogues. The fossil regions of Great Britain, an epitome of the world, have been well explored, and the statement of fact stands nearly as follows:—Leaving out of consideration all the shelly and lime-building tribes, the numbers of the other families of animals hitherto found and described are, in the various groups of the silurian system, eight genera of only one order of fishes; in the devonian, of two orders, there are under forty genera, and not many more species of fishes, in the carboniferous, of three orders, there are about fifty genera, and a hundred species of fishes; in the permian and triassic, of three orders, there are twenty genera, and fifty species of fishes and reptiles; in the oolitic, of four orders, there are sixty genera, and two hundred and twenty species of fishes, reptiles, and mammals; in the wealden, there are, of three orders, twenty-five genera, and thirty-eight species of fishes and reptiles; in the cretaceous, of six orders, there are fifty genera, and eighty species of fishes, reptiles, and birds; in the tertiaries, of seven orders, the genera are about one hundred and fifty, and two hundred and twenty species of fishes, reptiles, birds, and mammals: thus making in all about four hundred genera, and seven hundred species of the larger families of living creatures during the whole currency of the geological epochs. The current epoch contains, exclusive of microscopic organisms, nearly two millions of species of vegetable and animal bodies existing on the terraqueous globe; and of which there are about eight thousand species of fish alone existing in our present seas.