FACIES DEVELOPMENT AND BIONOMY. Facies is the combination of physical and biological char acteristics exhibited by a geological formation at a particular point. These are determined at the present time by climate, depth, tides, nature of medium, distance from shore. etc. (see Dis TRIBUTION OF ANIMALS; ECOLOGY; FAUNA; FLORA), and just as different types of facies are being developed in the ocean and on the land at the present time, so they have been developed during all past periods of geological history. It follows then that the deposits formed any one period may be represented in different regions by littoral, sublittoral, abyssal, corallic, estua rine, lacustrine, or terrestrial facies, and each of these facies will have its own distinctive fauna. Study of the life habits of modern organisms en ables us to restore the habits of extinct forms of life, and we arc able to portray with a considerable degree of correctness the conditions under which the ancient faunas lived, and consequently also to picture the physiography of past times. The
large majority of fossiliferoui rocks are of ma rine origin. and hence a study of modern marine organisms is essential to a proper understanding of the bio»olnie conditions of the past. Fresh water and terrestrial deposits are also claiming more attention than they formerly received: they with their peculiar faunas and floras occur chief ly in the INle,fozoic and Cenozoic formations.
BioNomv. Marine organisms are broadly di vided into pelagic. m. those that inhabit the open sea, and littoral. those that live in the vicinity of the coasts. to their modes of life they are divided into plankton. nekton, benthos.