THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 41 



in that mineral than the one dredged by the U. S. S. " Tuscarora " in lat. 

 38° 32' N,, long. 123° 42' W., which seemed to be the purest glauconitic sand 

 previously known. Here the glauconite is wholly in the form of grains (not 

 in that of casts), which are typically rounded in shape, and are ovoid and 

 elongated, or approach a spherical form. Most of them are coated with a 

 thin film of gray clayey matter, so that their real color can only be seen by 

 transmitted light, after the grains have been crushed in a mortar in order 

 to obtain particles sufficiently thin. The grains are not all identical ; some 

 are dark grass-green, some yellowish green, and half the bulk is transformed 

 into a reddish-brown matter, where the crypto-crystalUne structure is some- 

 times preserved when the transformation is not too far advanced. The mean 

 diameter of the grains is 0.25 mm., and the amount in which they are present 

 is to the other minerals something like ten to one. The other minerals de- 

 tected are quartz, and a plagioclase, probably andesine. Unlike the glauconite, 

 these particles are angular; their mean diameter is also 0.25 mm. 



Fine Washings (3.77 per cent) ; as already stated, this percentage is not 

 above doubt, as the deposit may have been subjected to washing. The fine 

 washings are composed of very minute particles of glauconite and quartz, 

 together with some green, very flocculent, amorphous matter. 



No. 2. Station 4631, 3rd November, 1904. 

 Lat. 6° 26' N. ; long. 81° 49' W. ; depth, 776 fathoms. 



GREEN MUD : grayish-green, very plastic and sticky when wet ; coherent 

 and forming hard lumps when dried. It contains pieces of black rock, one 

 of them 1 cm. in diameter. 



Calcium carbonate: 25.20 per cent, Foraminifera, both surface and 

 bottom living, for the greater part broken. Globigcrina, Pulvinulina, Rotalia, 

 Truncatulina, and Cristellaria are the most common genera. There are also 

 a good many Echinoid spines. 



Residue: 74.80 per cent: — 



Siliceous Organisms (25 per cent), mostly gray, clayey casts of Foramini- 

 fera. Dark-brown casts do not appear to be present in this deposit. Actual 

 siliceous organisms are here present in the form of Sponge spicules, which 

 are much less abundant than the gray casts. 



Minerals (25 per cent) ; besides one or two isolated particles of quartz, 

 minerals are mainly represented by rock fragments and glauconitic grains. 

 The rock fragments largely predominate, and vary much in size ; the aver- 



