212 
THE VOYAGE OF H.M.S. CHALLENGER. 
lu tliis analysis, even better than in those of the Radiolarian Ooze, the large part 
taken by the remains of siliceous organisms in the composition of the deposit is rendered 
’evident by the quantity of soluble silica. In the portion soluble in hydrochloric acid and 
treated with potash the soluble silica amounts to 67*92 per cent. Having regard to the 
low percentage of alumina and peroxide of iron, with which the silica and water lost 
on ignition might be combined, it must be admitted that amorphous silica exists in a free 
state, and that the water must be combined with • silica, thus forming hydrated silica, 
analogous to that which, as we have seen, forms the skeletons of Radiolarians. As the 
quantity of water is variable for hydrated silica, and as the loss on ignition compre- 
hends also organic substances, it would be useless to lay too much stress on the 
figures, but it may be said that they represent approximately the mean hydration of 
opals, viz., about 8 per cent. In this case the soluble silica may be said to make up 
about three-fourths of the deposit. With the exception of 19*29 per cent, of carbonate 
of calcium, which is chiefly derived from pelagic Foraminifera and shells of Molluscs, &c., 
the deposit may be regarded as very pure, for all the substances soluble in hydrochloric 
acid, except the silica, are represented by very small quantities, in comparison with what 
is met with in other deposits. In the specimen analysed there can have been but little 
argillaceous matter or ferric hydrate, and in the insoluble portion the anhydrous silicates 
are represented by only 4*72 per cent. The specimen taken for this analysis may have 
been exceptionally pure, for it must be remembered that in the large quantity dredged by 
the Challenger at this station there were many fragments of rocks of considerable size, 
and associated wdth these we would expect to find a larger quantity of argillaceous matter 
than is indicated in the above analysis. 
Another analysis of material from the same station is, properly speaking, one of those 
portions comprised in our Tables under the headings “siliceous organisms” and “fine 
washings.” The substance analysed had been treated with hydrochloric acid to remove 
the calcareous organisms, and therefore consisted as nearly as possible of siliceous organ- 
isms, chiefly Diatoms, but mixed w’ith these were a few Radiolaria and Sponge spicules. 
station. 
, 
Depth in 
Fatlioiiia. 
No. 
Loss. 
SiOa 
AI 2 O 3 
FC203 
CaO 
MgO 
BaO 
•K,0 
Na.^0 
PjOs 
Total 
157 
1050 
82 
5-85 
90-56 
1-31 
0-88 
0-33 
0-30 
0 20 
0-15 
0-40 
tr. 
99-98 
In this analysis, again, the high percentage of silicic acid shows the true nature of the 
deposit, and considering the percentage of water (loss) and the low percentage of all the 
bases, it may be concluded that almost all the portion of the deposit here under considera- 
tion is com|>o8cd of a form of hydrated silica derived from Diatom frustules and remains of 
other siliceous organisms, mixed with a very small quantity of ferruginous clayey matter. 
