222 THE ATLANTIC. [ CHAP. III. 
former they were calcareous. The radiolarian ooze, although 
consisting in great part of the tests of Radiolarians, contains even 
in its purest condition a very considerable proportion of red 
clay. Iam certainly inclined to accept an explanation of this 
second change, which was first suggested by Mr. Murray, and 
which is indeed almost a necessary sequel to his investigations. . 
Fig. 53.—Xiphacantha (sp.n.). From the surface. One hundred times the natural size. 
The skeleton only. 
We have every reason to believe, from a series of observa- 
tions as yet very incomplete, with the tow-net at different 
depths, that while foraminifera are apparently confined to a 
comparatively superficial belt, Radiolarians exist at all depths in 
the water of the ocean. At the surface and a little beneath it 
the tow-net yields certain species; when sunk to greater depths, 
additional species are constantly found ; and in the deposit at 
