DEEP-SEA DEPOSITS. 563 



in the Indian Ocean. It might have been thonght that these innu- 

 merable crystals of christianite came from the simple <lisintegra- 

 tion of volcanic rocks, with the paste of which they would have been 

 associated; but the forainiiiifers brought up from the deeps by the 

 dredge are completely enveloped with crystalline coverings of this 

 mineral, which proves the fact iiot to be so. The formation of the 

 zeolite is posterior to the deposit of tiie sediments engendered by the 

 transformation of volcanic substances which cover the bed of the sea. 



Crlnuconiie. — Among the mineral deposits found on the sea bottoms 

 is another hydrated silicate, known under the name of glauconite, which 

 has for its bases aluminium, protoxide of iron, and other metals. Its 

 mode of formation as well as the great extents on which it is found, 

 specially call attention to it. It takes the form of small grains of a 

 green color, and completely similar in form, dimension, and apijearance, 

 to the particles of the same mineral which abound in various geological 

 }»eri<)ds of the series of stratified rocks from the most ancient times to 

 the most recent. Glauconite thus plays an important part in space as 

 well as in time. The formation of this mineral in the great sea deeps, 

 brought to notice forty years ago by Bailey and Pourtales, has been 

 the object of many investigations, specially by Ehrenberg. 



Hydrated oxide of manganese {icad); hydrated oxide of iron {limonife). — 

 Two other species to be mentioned, which submarine chemistry has pro- 

 duced, and no doubt is still i>roducing, are the hydrated oxides of man- 

 ganese and of iron, which are specially observed in nodules. These sub- 

 stances are disseminated over the whole surface of the sea-bottom, but 

 specially in the red clay area. It is easy to understand this association ; 

 the volcanic rocks from which these clays are obtained containing 

 abundance of iron and manganese in their mineral constituents, jjeri- 

 dot, i)yroxen, and others. In consequence of their decomposition the 

 oxides are liberated in conformity with the reactions so ably demon- 

 strated by Ebelmen.* 



Among the organic and inorganic debris which in the red clay regions 

 serve as center to the ferro-mauganiferous concretions, the remains 

 of vertebrates have been frequently found. The bones thus found are 

 the most enduring portions of the skeleton, such as the tympanic bones 

 of the cetacea and the teeth of the shark. Just as we see the calcare- 

 ous organisms eliminated at great depths, so also it is found that, 

 except these massive portions, all bones of vertebrates are missing in 

 the deep sediments. Some of these remains of vertebrates belong to 

 extinct species. 



Phosphate of lime. — Off the cape of Good Hope, the dredge brought 

 up from various depths of between 200 and 4,000 meters, quartzy and 

 glauconitic muds, charged with the remains of various organisms, some 



* In .an appendix Mr. Gibson points out, by the aid of spectroscopic analysis, in tne 

 manganese nodules, traces of various »deuients, barium, strontium, lithium, titanium, 

 vanadium, and thallium. 



