Mesozoic and Ccunozuic Geology and Paloeontology. 39 



in the same proportion. The Mid- Atlantic swarms with pelagic mol- 

 lusca; and in moderate depths, the shells of these are constantly mixed 

 with the globigerina ooze, sometimes in number sufficient to make up 

 a considerable portion of its bulk. It is clear that these shells must 

 fall in equal numbers upon the red cla}'; but scarceh' a trace of one of 

 them is ever brought up b_y the dredge on the red cla}' area. It might 

 be possible to explain the absence of shoU-secreting animals living on 

 the bottom by the supposition that the nature of the deposit was in- 

 jurious to them; but the idea of a current sufficiently strong to sweep 

 them awa}?-, if falling from the surface, is negatived by the extreme 

 fineness of the sediment which is being laid down. The absence of 

 surface shells appears to be intelligible only on the supposition that 

 they are in some wa}^ removed b}^ chemical action. 



"We conclude, therefore, that the red cla^^ is not an additional sub- 

 stance introduced from without, and occupying certain depressed re- 

 gions on account of some law regulating its deposition; but that it is 

 produced by the removal, by some means or other, over these areas, of 

 the carbonate of lime, which forms probabl}' about 98 per cent, of the 

 material of the globigerina ooze. "We can trace, indeed, every succes- 

 sive stage in the removal of the carbonate of lime, in descending the 

 slope of the ridge or plateau where the globigerina ooze is forming, to 

 the region of the clay; we find, first, that the shells of pteropods and 

 other moUusca, which are constantly falling on the bottom, are absent; 

 or, if a few remain, they are brittle and yellow, and evidentl}' decaying 

 rapidly. These shells of mollusca decompose more easily, and disap- 

 pear sooner than the smaller, and apparently more delicate shells of 

 rhizopods. The smaller foraminifera now give way, and are found in 

 lessening proportion to the larger; the coccoliths first lose their thin 

 outer border and then disappear; and the clubs of the rhabdoliths get 

 worn out of shape, and are last seen, under a high power, as minute 

 C3-linders scattered over the field. The larger foraminifera are at- 

 tacked, and instead of being vividlj' white and delicately sculptured, 

 the}' become brown and worn, and finally thej- break up, each accord- 

 ing to its fashion: the chamher-waWs of Glob igei'ina fall into wedge- 

 shaped pieces, which quickly disappear; and a thick rough crust 

 breaks away from the surface of Orbulina, leaving a thin inner sphere, 

 at first beautifully transparent, but soon becoming opaque and crumb- 

 ling awa3% 



" In the mean time, the proportion of the amorphous, red cla}^ to the 

 calcareous elements of all kinds increases, until the latter disappear, 

 with the exception of a few scattered shells of the larger foraminifera, 



