Page:Popular Science Monthly Volume 44.djvu/483

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469
PHYSICAL CONDITIONS OF THE DEEP SEA.

ly flowing water, for if they did so they would soon be smothered by the fine mud that composes the floor of all the deep seas. In fact, anemones of the type presented by such forms as Sicyonis crassa are only fitted for existence in sluggish or still water.

Another character that must be taken into consideration is that presented by the floor of the great oceans. The floor of the ocean, if it were laid bare, would probably present a vast undulating plain of fine mud. Not a rock, not even a stone, would be visible for miles. The mud varies in different parts of the globe according to the depth, the proximity to land, the presence of neighboring volcanoes, or the mouths of great rivers.

The globigerina ooze is perhaps the best known of all the different deep-sea deposits. It was discovered and first described by the officers of the American Coast Survey in 1853. It is found in great abundance in the Atlantic Ocean in regions shallower than

PSM V44 D483 Globigerina ooze.jpg
Fig. 3.—Globigerina Ooze. (After Agassiz.)

2,200 fathoms. Deeper than this it gradually merges into the "red mud." It is mainly composed of the shells of foraminifera, and of these the different species of globigerina are the most abundant. It is probably formed partly by the shells of the dead foraminifera that actually live on the bottom of the ocean and partly by the shells of those that live near the surface or in intermediate depths and fall to the bottom when their lives are done. So abundant are the shells of these protozoa that nearly ninety-five per cent of the globigerina ooze is composed of carbonate of lime. The remaining five per cent, is composed of sulphate and phosphate of lime, carbonate of ammonia, the oxides of iron and manganese, and argillaceous matters. The oxides of iron and manganese are probably of meteoric origin; the argillaceous matter may be due to the trituration of lumps of pumice stone and to the deposits caused by dust storms.

Globigerina ooze may be found on the floor of the ocean at