A subsequent uplift of the coast will be accompanied by a recession of the sea, and when later dissected by nature for our inspection, the order of superposition and the individual character of each of the deposits may be studied at leisure. From such studies it has been found that along with the inorganic deposits there are often found the remains of life in the hard parts of such invertebrate animals as the mollusks and the crustacea. These so-called _fossils_ represent animals which were gradually developed from simpler to more and more complex forms; and they thus serve the purpose of successive page numbers in arranging the order of disturbed strata, at the same time that they supply the most secure foundation upon which rests the great doctrine of evolution.
=The basins of earlier ages.=—It was the great Viennese geologist, Professor Suess, who first pointed out that in mountain regions there are found the thickest and the most complete series of the marine deposits; whereas outside these provinces the formations are separated by wide gaps representing periods when no deposits were laid down because the sea had retired from the region. The completeness of the series of deposits in the mountain districts can only be interpreted to mean that where these but lately formed mountains rise to-day, were for long preceding ages the basins for deposition of terrigenous sediments. It would seem that the lithosphere in its adjustment had selected these earlier sea basins with their heavy layers of sediment for zones of special uplift.
=The deposits of the deep sea.=—Outside the continental slope, whose base marks the limit of the terrigenous deposits, lies the deeper sea, for the most part a series of broad plains, but varied by more profound steep-walled basins, the so-called “deeps” of the ocean. As shown by the dredgings of the _Challenger_ expedition and others of more recent date, the deposits upon the ocean floor are of a wholly different character from those which are derived from the continents. Except in the great deeps, or between depths of five hundred and fifteen hundred fathoms, these deposits are the so-called “ooze”, composed of the calcareous or chitinous parts of algæ and of minute animal organisms. The pelagic or surface waters of the ocean are, as it were, a great meadow of these plant forms, upon which the minute crustacea, such as globigerina, foraminifera, and the pteropods, feed in countless myriads. The hard parts of both plant and animal organisms descend to the bottom and there form the ooze in which are sometimes found the ear bones of whales and the teeth of sharks.