THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 163 



under ordinary circumstances expect to find a Globigerina Ooze. Indeed, in 

 the case of Station 4719, the adjacent stations, where tlie depth is quite 

 similar, give Globigerina Oozes containing over 50 per cent of calcium car- 

 bonate. It seems, therefore, that in these exceptional cases some hypogene 

 action has taken place, resulting in the removal of the whole of the calcium 

 carbonate shells and remains from the deposit. That some such action had 

 taken place at the bottom of the sea was indicated at a few stations during the 

 " Challenger " expedition, but from the larger number of instances revealed 

 by the examination of Dr. Agassiz's collections this explanation seems now 

 clearly necessary. Again, at Station 4531, where the percentage of calcium 

 carbonate is 72, the calcareous shells have disappeared, and the deposit con- 

 sists of a large quantity of comminuted particles of calcium carbonate together 

 with coccoliths and Tunicate spicules. Probably this calcium carbonate has 

 all been derived from the shells of marine organisms, but these have disap- 

 peared through some hypogene action. Possibly there may also have been a 

 chemical precipitation of calcium carbonate. 



The mineral particles found in Red Clay and Globigerina Ooze are nearly 

 always of volcanic origin, and we may once more draw attention to the great 

 role that palagonite and allied minerals play in the southern Pacific Ocean. 

 This distribution of decomposed basic volcanic elements coincides with the 

 frequent occurrence of phillipsite, and explains the presence of this mineral 

 in Globigerina Ooze as well as in Red Clay, its origin being thus independent 

 of a question of great depth. The same may be said of manganese concre- 

 tions and nodules; being generally found far from land, the origin of the 

 manganese is not to be sought for in the products of continental erosion, but 

 in those of the decomposition of the volcanic elements we have found to be 

 so widely distributed. 



It must be remembered that the Red Clay of the deeper parts of the ocean 

 has no definite composition. It is made up of materials from very different 

 sources, as we have just seen. In the South Pacific basic volcanic rocks, like 

 sideromelan and palagonite, predominate ; in the North Pacific the triturated 

 fragments of pumice are most abundant. In some parts of the Atlantic the 

 Red Clay receives additions which have a continental origin, as in the case 

 of sand grains transported by the Harmattan Winds off the west coast of 

 Africa. 



Dr. W. A. Caspari, who has been assisting in chemical examination of the 

 deposits in the " Challenger " Office, has prepared some notes upon his exami- 



