REPOET ON THE DEEP-SEA DEPOSITS. 
207 
Portion 
SOLUBLE IN 
HCl. 
Portion 
INSOLUBLE 
IN HCl. 
d 
o 
sj 
O 
ft 
No. 
Loss. 
SiOj 
AI2O3 
Fe 203 
Mn02 
CaCOs 
CaSO^ 
Ca 32 P 04 
MgCOs 
Total. 
SiOj 
AI2O3 
CaO 
MgO 
Total. 
265 
2900 
28 
4-30 
38-75 
6-75 
11-20 
0-57 
2-54 
0-29 
0-65 
2-46 
63-21 
21-02 
6-19 
3-09 
1-85 
0-34 
32-49 
274 
2760 
29 
7-41 
46-50 
8-32 
14-24 
3-23 
3-89 
0-41 
1-39 
1-50 
79-48 
9-52 
2-20 
0-75 
0-39 
1-25 
13-11 
No. 28 is of material oMained in the dredge, No. 29 as it came up in the trawl. 
These analyses again show, from the totals of the soluble and insoluble portions and by 
the percentages of the various substances, a great variability in the deposit, depending 
upon the nature of the materials mixed up with the skeletons of the Eadiolaria and other 
siliceous organisms. On comparing these analyses with those of the Eed Clay, we find h 
much larger percentage of soluble silicic acid in this deposit than in the Eed Clay, the 
deep-sea deposit with which it is most nearly analogous. In one of the above analyses 
the soluble silica rises to 46'50 per cent.; admitting that a part comes from the hydrated 
silicates forming the argillaceous matter, from the zeolitic crystals which are very 
abundant in this deposit, or from the action of the acid and potash on the anhydrous 
silicates, still a very large part of the silica in the soluble portion of the analysis must 
come from the skeletons of the Eadiolarians, Diatoms, and Sponge spicules. In fact, 
the examination of these siliceous remains between crossed nicols show them to be 
composed of amorphous silica ; their loss on ignition shows also that they contain water 
in variable proportions, like opal, some specimens of which lose on calcination from 8 to 9 
per cent., and in some cases as much as 20 per cent, of their weight. This hydrated 
silica, more or less easily attackable by various chemical agents, is almost entirely removed 
by caustic potash.^ 
The water shown in the analyses must also be regarded as being associated partly 
with the silica in the siliceous organisms, as well as in combination with the iron and 
alumina. The percentages of alumina and iron indicate that clay and limonite are 
present in considerable quantities. What has been said with reference to the analyses 
of the Eed Clays applies also here to the manganese, carbonate, sulphate, and phos- 
phate of lime, and carbonate of magnesia. The relatively small quantity of carbonate 
of calcium is explained by the great depth of the Eadiolarian Oozes, for, as has 
already been pointed out, carbonate of lime gradually disappears from the deposits 
with increasing depth. The division referring to the insoluble part shows anew the 
presence of insoluble silica, of silicates, and of silicated rocks containing alumina, iron, 
1 For a description of the various Eadiolarian. spicules and their chemical composition, see Haeckel, “ Eeport on 
the Eadiolaria,” Zool. Chalk Exp., part xl. pp. Ixviii et seq. See also Thoulet, “ Sur les spicules siliceux d’eponges 
vivantes,” Gomptes Rendus, tom. xcviii. p. 1000, 1884, and the Challenger Eeports on the Hexactinellida, Tetractinellida, 
and Monaxonida. 
