1. We are already familiar with a marine Gryphæa, and different Terebratulæ, also marine shell-fish, which do not, however, live near shore. 2. Also the greatest depth which has been reached with the rake or the dredge is not destitute of molluscs, since we find there a great number which only live at this depth, and without instruments to reach and bring them up we should know nothing of the _cones_, _olives_, Mitra, many species of Murex, Strombus, etc. 3. Finally, since the discovery of a living Encrinus, drawn up on a sounding line from a great depth, and where lives the animal or polyp in question, it is not only possible to assure ourselves that at this depth there are other living animals, but on the contrary we are strongly bound to think that other species of the same genus, and probably other animals of different genera, also live at the same depths. All this leads one to admit, with Bruguière,[78] the existence of deep-water shell-fish and polyps, which, like him, I distinguish from littoral shells and polyps. "The two sorts of monuments of which I have above spoken, namely, littoral and deep-sea fossils, may be, and often should be, found separated by different beds in the same bank or in the same mountains, since they have been deposited there at very different epochs. But they may often be found mixed together, because the movements of the water, the currents, submarine volcanoes, etc., have overturned the beds, yet some regular deposits in water always tranquil would be left in quite distant beds.... Every dry part of the earth's surface, when the presence or the abundance of marine fossils prove that formerly the sea has remained in that place, has necessarily twice received, for a single incursion of the sea, littoral shells, and once deep-sea shells, in three different deposits--this will not be disputed. But as such an incursion of the sea can only be accomplished by a period of immense duration, it follows that the littoral shells deposited at the first sojourn of the edge of the sea, and constituting the first deposit, have been destroyed--that is to say, have not been preserved to the present time; while the deep-water shells form the second deposit, and there the littoral shells of the third deposit are, in fact, the only ones which now exist, and which constitute the fossils that we see."