378 Quaricrly Journal of Conchology. 



zones of depth — the "abyssal" for depths between loo-iooo 

 fathoms, and '"benthal"' for depths of 1000 fathoms and more. 



The author is of opuiion that the distribution of the deep- 

 sea mollusca is caused by submarine currents, and that the iVrctic 

 and Antarctic currents do not extend beyond the equator. 



The theory of the continuity of the chalk which has had 

 many able advocates; is discussed by Dr. Jeffreys in the two aspects 

 of mineral composition, and the organisms belonging to each. 



The Chalk consists almost entirely of Carbonate of Lime, 

 while according to an analysis of the late Prof D. Forbes of a 

 sample of Atlantic ooze, procured from a depth of 1443 fathoms, 

 it contained scarcely 50 per cent, of that substance; and one of 

 its most able advocates, Sir Wyville Thomson, admits that more 

 careful examination shows important differences. 



The organisms considered by Dr. Jeffreys are naturally the 

 Mollusca regarded by Lyell as the "highest or most specialized 

 organisms" on which geological reasonings are founded. 



The apparent resemblance of the abyssal and benthal ooze to 

 the ancient chalk has led geologists to the conclusion that the 

 chalk fauna had lived in deep water. From a list prepared 

 by Mr. Etheridge for Dr. Jeffreys and reproduced in the address, 

 it is apparent that all the genera enumerated in the list were 

 comparatively shallow water forms, not a single Leda, Fecc/iioh'a, 

 Ni'cera, Bulla or any of the Sokiwconchia occur in the upper or 

 white chalk although they inhabit the deep sea ooze and especially 

 characterize the modern deposit, Mr. Woodward also remarks 

 that the Crustacea of the chalk are shallow water forms. 



The white chalk is in many ]Dlaces composed of Ghbigcfi/ics, 

 Szc, all of which inhabit at present the surface of the sea. 

 According to Dr. Wallich, Globigerincc are found in all latitudes 

 and at all depths ranging from 50-3000 fathoms. 



