306 



THE MICROSCOPE AND ITS REVELATIONS. 



Mention lias already been made ( 480) of the fact that a large propor- 

 tion of the North Atlantic sea-bed has been found to be covered with an 

 * ooze ' chiefly formed of the shells of GloUgerince; and this fact, first deter- 

 mined by the examination of the small quantities brought up by the sound- 

 ing apparatus, has been fully confirmed by the results of the recent ex- 

 ploration of the Deep-sea with the dredge; which, bringing up half a ton 

 of this deposit at once, has shown that it is not a mere surface-film, 

 but an enormous mass whose thickness cannot be even guessed at. 

 "Under the Microscope," says Prof. Wyville Thomson 1 of a sample 

 of 1J cwt. obtained by the dredge from a depth of nearly three miles, 

 "'the surface-layer was found to consist chiefly of entire shells of Cflobi- 

 (jerina bulloides, large and small, and of fragments of such shells mixed 

 with a quantity of amorphous calcareous matter in fine particles, a little 

 fine sand, and many spicules, portions of spicules, and shells of Radio- 



FIG. 489. 



Microscopic Organisms in Chalk from Gravesend: a, 6, c, d, Textularia globulosa; e, e t e, Rota- 

 liaaspera; /, Textularia aculeata; g, Planularia hexas; h, Navicula. 



luria, a few spicules of Sponges, and a few frustules of Diatoms. Below 

 the surface-layer the sediment becomes gradually more compact, and a 

 slight gray color, due, probably, to the decomposing organic matter, be- 

 comes more pronounced, while perfect shells of Globigerina almost dis- 

 appear, fragments become smaller, and calcareous mud, structureless, 

 and in a fine state of division, is in greatly preponderating proportion. 

 One can have no doubt, on examining this sediment, that it is formed 

 in the main by the accumulation and disintegration of the shells of Glo- 

 bigerina; the shells fresh, whole, and living, in the surface-layer of the 

 deposit; and in the lower layers dead, and gradually crumbling down by 

 the decomposition of their organic cement, and by the pressure of the 

 ] ayers above." This white calcareous mud also contains in large amount 



1 " The Depths of the Sea," p. 410. 



