Tabular View of Oceans and Seas

Opinions are still varied as to the time necessary for the forma tion of I cm. or 1 ft. of deep sea deposit. It is generally believed that the red clay accumulates extremely slowly because sharks' teeth and whales' ear-bones which serve as nuclei in it belong, in some cases, to extinct species and are not found in the globigerina ooze, although there is no reason to suppose that at any one time they were unequally distributed over the ocean floor. Cable en gineers report that a layer of globigerina ooze 2 cm. thick can be formed in ten years. For 2 cm. of coccolith ooze to be formed, however, it is computed that 4,000 years are necessary.

The frequently observed stratification within a sample is also important. All samples are not homogeneous, one of 5o cm. depth can include very varied deposits. In some samples sand which can be deposited only near a coast is found under a layer of globigerina ooze, whence it is evident that the study of marine deposits is of great importance in connection with investigations of geomorpho logical evolution.

Permanence of the Ocean Beds.

There are no known sedimentary rocks that appear to have been deposited at the bottoms of oceans comparable in depths with those we know— that is, there are no formations known that resemble, for instance, the globigerina ooze now being deposited on the Atlantic floor. On the other hand, the geographical distribution of many species of plants and animals points very decidedly towards the existence in the past of land connections between the various continents, and this evidence cannot be put aside. It was therefore given as

another theory by Neumayer, Frech and others (1885, 1902) that, in the north and south Atlantic, in the central part of the Indian ocean, and possibly in the central part of the Pacific, there were, during the Mesozoic period, extensive land regions that have now subsided. Thus there are indications that large regions of continental land have been depressed to form the floors of deep oceans, but there are no clear indications that deep ocean beds have ever been elevated to form dry land.

A third hypothesis set out by A. Wegener in 1915, suggests that the great continental land elevations actually slip on the plastic layer beneath. The Atlantic basin has been formed by the slipping westward of the Americas. The coastal mountain ranges on the Pacific margin of the Americas were formed by the crumpling of the crust under the westward drift of the American continents, and so on. The hypothesis requires that there should be evidence of progressive change of longitude. Observed changes are doubted. It also requires some stress-difference under which the continental land masses yield and shift place relative to the earth-axis. All these three very different theories—that of permanence, that of bridge continents and that of slipping continents—have their difficulties and objections. It follows that there can be no agree. ment as to the age of the oceans.