562 DEEP-SEA DEPOSITS. 



that finally, far from the surface nothing- is found but the red clay, 

 entirely without lime, under organized form. The shells of pteropods 

 disappear first, then the envelopes of the foraminifers, Avliich a coating 

 of organic matter seemed to protect. It seems probable that this elimi- 

 nation of carbonate of lime is due to the action of carbonic acid dis- 

 solved in the deep laj^ers of oceanic waters, where its chemical activity 

 is reinforced by the enormous jiressure that reigns. The silica of the 

 organisms resists the best, and it is thus that their skeletons, spicules, 

 and other siliceous vestiges accumulate on the bottom. 



Everything seems to indicate that the formation of red clay is essen- 

 tially due, like that of most of the other minerals which are to come 

 under our notice, to the decomposition of the incoherent and very 

 tenuous volcanic productions which abound on all the great ocean beds. 

 In the regions where red clay shows its most distinct characteristics 

 this transformation of the volcanic rocks into clayey matter may be 

 followed through its successive phases. The clayey matter is the direct 

 product of a chemical decomposition, si^ecially of the silicates, which 

 are basic and in part represented by the pumice and the volcanic 

 glasses. 



Ebelmeu,* so prematurely taken away from science, which he 

 endowed with discoveries full of genius, was the first to show how 

 the aluminous silicate rocks, principally tliose of eruptive origin, so 

 frequent at the surface of the globe, are decomposed by the mere action 

 of the atmosphere; their protoxides, such as lime and magnesia, are car- 

 ried off iu a state of carbonate, while the alumina is concentrated with 

 the silica, so as to form a hydrated silicate of the clay family. 



The same slow reactions seem to take place upon the ocean bottom at 

 the expense of the volcanic silicates, aided perhaps by the chemical 

 action of the sea water. Certain fusible muds contain, very probably, 

 portions still undecoraposed, but in such fine dust that they may be 

 confounded with the clay. It has been so with the muds that I have 

 obtained by experiments upon the trituration of feldspar; they are so 

 finely divided that they are soft as clay to the touch and possess the 

 same plasticity. 



Zeolites. — Notwithstanding the very low temperature which prevails 

 at the ocean bed, the <jhemical reactions seem to produce sharply-crys- 

 talized minerals, the most remarkable of which, without doubt, belongs 

 to the double hydrated silicates, known under the name of zeolites. 

 These zeolites are met with in great abundance under the form of 

 small isolated crystals^ simple or grouped geometrically, often in 

 spherules of hardly a half millimeter in diameter, and in all cases con- 

 fused with the clay. Crystallographic and chemical analyses show 

 that they must belong to the species called chrisfianite or pMUppsite. 

 This discovery was made in the center of the Pacific. It was repeated 



*See the article by Mr. Chevrenl \nt\\QJourrial des Savants, 1884, p. 104. 



