Page:The New International Encyclopædia 1st ed. v. 15.djvu/282

PALEONTOLOGY. eareous skeletons. Certain types of moUusks are characteristic of the littoral zone; oysters, mussels, the heavy clams, limpets, clitons, Lil- toriua-like shells, the boring laniellibranchs, and here belong also the coarse marine alga-, crabs, and auoniurans. The littoral facies is the most important of all, for most of the fossiliforoiis rocks have been formed in the shallow water near the shore and on the continental shelf, and also because preeniiuently, in its peculiar development of corallic facies, it contains the largest fauna.

.SrBLiTTOK.L Facies includes those deposits formed in the deeper water at a distance from the coast. It merges on the one side into the littoral and on the other into the abyssal facies. It contains the remains of pelagic ( plankton and nekton) organisms which after death have sunk to the bottom, and also of those benthonic or- ganisms of the deeper waters. Here are Included fish, aramonoids. pteropods, gra)iti)lites, many foraminifers. radiolariaus, and many echinoderms. mollusks. and brachiopods of more delicate build than those found in the littoral facies. Many of the pelagic organisms enjoyed very wide distri- bution, as the graptolites, and hence afrord excel- lent index fossils for correlative purposes. Ex- amples of sulilittnral facies are the graptolite shales of the Ordovician, goniatite, and ammonite limestones and shales of the Upper Paleozoic and llesozoic, and many pteropod limestones, like the Styliolina limestone of the Devonian.

Abyss.l Facies. Here are included the de- posits of the deep sea, consisting of very fine grain sediments of various types. ( See Ooze. ) The existence of abyssal sediments among the rocks of the earth's crust has been strongly denied by some writers. It is, however, difficult to assign certain geological formations to any other category. Such are the chalk deposits of the Cretaceous, the Upper Paleozoic radiolarian cherts of New South Wales, and those of .Jurassic age in the .Vlps, and the Aptychus sliales of the Alps, all of which are very similar to the abyssal deposits of the present day.

Corallic Facies. This is really a phase of the littoral facies, but as its characteristics are so distinct, and as its development depends upon the absence of many of those features associated with the normal littoral facies, it deserves special con- sideration. The conditions under which corals form reefs at the present time are a warm tem- perature, shallow water not more than 125 feet deep, and pure sea-flater entirely free from mud and from inllowing fresh water. The other or- ganisms living about the coral reef require the same conditions. These conditions existed also during the formation of the Paleozoic and ileso- zoic and Tertiary coral reefs, for the rocks of these fossil reefs are free from traces of mud and clay.

EsTi'ARiNE Facies embraces the deposits and faunas of lagoons and estuaries. The sediments are usually irregularly bedded muddy sands and clays. Here is found a commingling of brackish water types with marine organisms, freshwater and terrestrial types. A fine example of such an estuarine facies' is afforded by the Lower Car- boniferous nodule-hearing shales of llazon Creek, near llorris. 111., described by Meek and Wor- then. Scudder. and others. The nodules have furnished a very large congeries of plants and animals. There are represented here ferns, am- phibians, fish, insects, spiders, scorpions, myria- pods. eurypterids, crustaceans, aipiatic worms, la- niellibranchs of marine and fresh-water tyjics. gastropods of freshwater, marine, and terrestrial types. No strictly marine types, like crinolds and brachiopods, occur here, those present being spe- cies which could live in brackish water. Other examples of estuarine facies are found in the Carboniferous, Mesozoic, and Tertiary formations of Kuroi)e. In all probability many of the coal- measure swamps were of estuarine nature, for sections through the beds show alternations of marine and fresh or brackish water faunas. Fresh-Water Facies appears first in the Car- boniferous in the form of swamp deposits, now turned into coal. In these deposits are abundant fossil plants of various types, and remains of freshwater mollusks, insects, etc., and also of am- phibians and fish. In the Mesozoic. and in more jnonounced degree in the Tertiary, lacustrine de- ])osits are largely developed. They may be rec- ognized by their contained fresh-water shells: Paludina, Gimiobasis, Planorbis, Limnsea, Unio, and.

odonta. They have afforded also the far more important and more interesting vertebrate remains, such as the dinosaurs, birds, and mam- mals. Terrestrial fades, represented by deposits of Hood plain, desert, and i>rairie, do not as a rule afford many fossil remains. The loess, a re- cent a<'cuinulation of dust and river mud, con- tains land and fresh-water shells; and the While Kiver Miocene clays of Colorado, containing fine- ly- preserved vertebrates, are thought to have been accumulated largely as dust upon a Tertiary prairie.

Composite Facies. The fossil elements of a fauna may be distinguished as autochthonous, or those which naturally belong in the deposits where found and which have been buried where they lived or where they fell to the bottom ; and heterochthonous, or those which owe their en- tombment to the agencies of currents or other means of transportation, and have been buried far from their natural habitats. The autoch- thonous fossils are the more reliable for zonal correlation, while the heterochthonous fossils in- dicate the nature of preexistent faunas and the proximity of neighboring faunas of different facies.

A.xciEXT Climate and Paleoceoiiraimiy. Cli- matic zones arc thought to have existed as early as Cambrian time and to have continued through the Silurian and Devonian periods. The Euro- pean and North American faunas of the.se pe- riods can be separated into northern and southern types which are quite distinct, the various genera having representative species in each zone. The courses of oceanic currents have been indicated for the early and late Ordovician by Matthew and Kuedemann. Other eviilenee regarding the climate of the Paleozoic is derived from study of the distrilnition of the fossil coral reefs of the Silurian, and of the plants of the Carboniferous. The Silurian coral reefs are found in high lati- tudes and indicate rather warm temperatures for those regions, and the structure of the Car- boniferous tree trunks points to a remarkable uni- formity of the seasons during that ))eriod. Neu- mayr has tried to demonstrate that the .Jurassic ancl Cretaceous faunas show the inlluence of well- marked climatic zones which extended in belts around the globe independent of the continental barriers, but his results have not been confirmed