animals of the same great molluscan group than the present time. Our British group of recent marine shells falls somewhat short of _four_ hundred species;[19] whereas the group characteristic of the older Miocene deposits, largely developed in those districts of France which border on the Bay of Biscay, and more sparingly in the south of England, near Yarmouth, comprises more than six hundred species. Nearly an equal number of still older shells have been detected in a single deposit of the Paris basin,--the _Calcaire grossier_; and a good many more in a more ancient formation still, the London Clay. On entering the Chalk, we find a yet older group of shells, wholly unlike any of the preceding ones; and in the Oolite and Lias yet other and different groups. And thus group preceded group throughout all the Tertiary, Secondary, and Palæozoic periods; some of them remarkable for the number of species which they contained, others for the profuse abundance of their individual specimens, until, deep in the rocks at the base of the Silurian system, we detect what seems to be the primordial group, beneath which only a single animal organism is known to occur,--the _Oldhamia antiqua_,--a plant-like zoophyte, akin apparently to some of our recent sertularia, (See fig. 5, page 48.) Each of the extinct groups had, we find, a beginning and an end;--there is not in the wide domain of physical science a more certain fact; and every species of the group which now exists had, like all their predecessors on the scene, their beginning also. The "infinite series" of the atheists of former times can have no place in modern science: all organic existences, recent or extinct, vegetable or animal, have had their beginning;--there was a time when they were not. The geologist can indicate that time, if not by years, at least by periods, and show what its relations were to the periods that went before and that came after; and as it is equally a recognized truth on both sides of the controversy, that as something now exists, something must have existed forever, and as it must now be not less surely recognized, that that something was not the race of man, nor yet any other of the many races of man's predecessors or contemporaries, the question, What then was that something? comes with a point and directness which it did not possess at any former time. By what, or through whom, did these races of nicely organized plants and animals begin to be? Hitherto at least there has been but one reply to the question originated on the skeptical side. All these races, it is said, have been _developed_, in the long course of ages, into what they now are, as the young animal is developed in the womb, or the young plant is developed from the seed. Topsy, in the novel, "'spected that she was not made, but growed;" and the only class of opponents which the geological theist finds in the field which his science has laid open to the world is a class that hold by the philosophy of Topsy.