THE FLOOR OF THE OCEAN BOSWELL 285 



these deposits from all over the ocean floor brings out the fact that 

 (if we except certain occurrences not very far from land, or wind- 

 borne, as mentioned previously) the detrital minerals are those con- 

 fined to igneous rocks and frequently to lavas. Minerals which could 

 have been derived only from ancient sedimentary and metamorphic 

 rocks, like those which make up the continents, are strikingly rare. 



In the reports of the Challenger expedition some 40 or more minerals 

 were recorded from deep-sea deposits. All could have been derived 

 from volcanic or intrusive rocks, or by growth in place: not one species 

 is peculiar to continental rocks. The general impression given by the 

 assemblage of minerals is intensified by the oft-recorded presence of 

 volcanic glass, tuff, palagonite and pumice. It would be inappropriate 

 to a general review such as this to cite long lists of minerals or to 

 describe their characters. It is probably of more interest to pass on 

 to a brief consideration of some of the newly-constituted minerals 

 now being formed on the sea floor. 



The problem of the mode of formation of such authigenic minerals 

 in sediments has long fascinated geologists. The term authigenic 

 denotes those minerals which have been formed in place, either 

 contemporaneously with the sediment or at a later date, as distinct 

 from the detrital minerals derived from the breaking-up of preexisting 

 rocks. The Challenger expedition discovered several authigenic 

 minerals in deep-sea deposits, among them being glauconite, calcium 

 phosphate, phillipsite, and other zeolites, and manganese oxide (in 

 manganese nodules). Among similar minerals, believed in some cases 

 to be of authigenic origin in ancient sedimentary rocks, are soda- 

 felspar (albite), potash-felspar (orthoclase and microcline), chlorite, 

 epidote, pseudo-sillimanite, sphene, tourmaline, and others, many 

 being somewhat complex silicates. We still hope that a more inten- 

 sive study of deep-sea sediments may throw light on their mode of 

 origin and perhaps even reveal them in actual process of formation. 

 Recently, two interesting and unexpected authigenic minerals new to 

 science have been discovered by Messrs. F. A. Bannister and M. Hey, 

 in samples collected by the Scotia from the Weddell Sea. From a 

 careful study of the chemical composition, optical properties and 

 X-ray spectrograms of some minute crystals found in the samples, 

 these investigators have described "envelope" crystals of a calcium 

 oxalate dihydrate from a depth of 2,400-2,700 fathoms. Somewhat 

 similar crystals have been found in cells of plants, in the gall of mam- 

 mals and fish, and in renal calculi. The chemical composition of these 

 deep-sea crystals suggests an origin in which organic processes played 

 a part. They appear to have been formed in muds on the sea-bottom, 

 here in an area of increased salinity, corresponding to a slight under- 

 saturation of calcium carbonate. A second group of crystals, similarly 

 investigated, proved to have the composition of hydrated calcium 



