=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. In the deeps of the ocean, none of these vegetable or animal deposits are being laid down, but only the so-called “red clay”, which is believed to represent decomposed volcanic material deposited by the winds as fine dust on the surface of the ocean, or the product of submarine volcanic eruption. From the absence of the ooze in these profound depths, the conclusion is forced upon us that the hard parts of the minute organisms are dissolved while falling through three or four miles of the ocean water. READING REFERENCES FOR CHAPTER IV J. S. DILLER. The Educational Series of Rock Specimens collected and distributed by the United States Geological Survey, Bull. 150 U. S. Geol. Surv., 1898, pp. 1-400. L. V. PIRSSON. Rocks and Rock Minerals. Wiley, New York, 1908. SIR JOHN MURRAY. Deep-sea Deposits, Reports of the _Challenger_ expedition, Chapter iii. L. W. COLLET. Les dépôts marins. Doin, Paris, 1907 (Encyclopédie Scientifique). CHAPTER V CONTORTIONS OF THE STRATA WITHIN THE ZONE OF FLOW