On a Piece of Chalk 85 



in making their burial journey from the surface of the 

 Atlantic to the bottom. 



But if the Radiolaria and Diatoms are thus rained 

 upon the bottom of the sea, from the superficial layer 

 of its waters in which they pass their lives, it is ob- 5 

 viously possible that the Globigerina may be similarly 

 derived; and if they were so, it would be much more 

 easy to understand how they obtain their supply of food 

 than it is at present. Nevertheless, the positive and 

 negative evidence all points the other way. The skeletons 10 

 of the full-grown, deep-sea Globigennte are so remarkably 

 solid and heavy in proportion to their surface as to seem 

 little fitted for floating; and, as a matter of fact, they 

 are not to be found along with the Diatoms and 

 Radiolaria, in the uppermost stratum of the open ocean. 15 



It has been observed, again, that the abundance of 

 Globigerinte , in proportion to other organisms, of like 

 kind, increases with the depth of the sea; and that 

 deep-water Globigerina are larger than those which live 

 in shallower parts of the sea; and such facts negative 20 

 the supposition that these organisms have been swept by 

 currents from the shallows into the deeps of the Atlantic. 



It therefore seems to be hardly doubtful that these 

 wonderful creatures live and die at the depths in which 

 they are found.* 25 



However, the important points for us are, that the 

 living Globigerirue are exclusively marine animals, the 

 skeletons of which abound at the bottom of deep seas; 



* During the cruise of H.M.S. Bulldog, commanded by Sir 

 Leopold M'Clintock, in 1860, living star-fish were brought up, 30 

 clinging to the lowest part of the sounding-line, from a depth of 

 1,260 fathoms, midway between Cape Farewell, in Greenland, 

 and the Rockall banks. Dr. Wallich ascertained that the sea- 

 bottom at this point consisted of the ordinary Globigerina ooze, 



