In 1810, Risso, in his work on the Ichthyology of Nice, laid the foundation of what has since been termed "bathymetrical" distribution, or distribution in depth, by showing that regions of the sea bottom of different depths could be distinguished by the fishes which inhabit them. There was the _littoral region_ between tide marks with its sand-eels, pipe fishes, and blennies: the _seaweed region_, extending from low- water-mark to a depth of 450 feet, with its wrasses, rays, and flat fish; and the _deep-sea region_, from 450 feet to 1500 feet or more, with its file-fish, sharks, gurnards, cod, and sword-fish. More than twenty years later, M.M. Audouin and Milne Edwards carried out the principle of distinguishing the Faunae of different zones of depth much more minutely, in their "Recherches pour servir à l'Histoire Naturelle du Littoral de la France," published in 1832. They divide the area included between highwater-mark and lowwater-mark of spring tides (which is very extensive, on account of the great rise and fall of the tide on the Normandy coast about St. Malo, where their observations were made) into four zones, each characterized by its peculiar invertebrate inhabitants. Beyond the fourth region they distinguish a fifth, which is never uncovered, and is inhabited by oysters, scallops, and large starfishes and other animals. Beyond this they seem to think that animal life is absent.[3] [Footnote 3: "Enfin plus has encore, c'est-à-dire alors loin des côtes, le fond des eaux ne paraît plus être habité, du moms dans nos mers, par aucun de ces animaux" (1. c. tom. i. p. 237). The "ces animaux" leaves the meaning of the authors doubtful.] Audouin and Milne Edwards were the first to see the importance of the bearing of a knowledge of the manner in which marine animals are distributed in depth, on geology. They suggest that, by this means, it will be possible to judge whether a fossiliferous stratum was formed upon the shore of an ancient sea, and even to determine whether it was deposited in shallower or deeper water on that shore; the association of shells of animals which live in different zones of depth will prove that the shells have been transported into the position in which they are found; while, on the other hand, the absence of shells in a deposit will not justify the conclusion that the waters in which it was formed were devoid of animal inhabitants, inasmuch as they might have been only too deep for habitation.