REPORT ON THE DEEP-SEA DEPOSITS. 
243 
The siliceous organisms range from 1 to 3 per cent., averaging 1‘40 j^er cent. 
The mineral particles consist of angular and rounded particles with a mean diameter 
of 0‘34 mm. They make up from 25 to 80 per cent, of these sands, the average per^ 
centage being 60. 
The fine washings vary from 2"35 to 18 '86 per cent., the average being 9’81 per cent. 
The following table gives the average percentage composition of the Challenger samples 
of Volcanic Sand, and comparison with the similar table given for the Volcanic Muds 
shows the difierence to consist chiefly in the larger number of mineral particles and the 
less abundance of the fine washings. 
Pelagic Foraminifera, . 
. 1300 
Carbonate of lime, 
Bottom-living Foraminifera, . 
3-80 
Other organisms, . 
. 11-99 
28-79 
Siliceous organisms. 
1’40 
Residue, 
Minerals, .... 
. 60-00 
Fine washings. 
9-81 
71-21 
100-00 
The mineral fragments in these muds and sands are variable as to their nature, being 
determined by the mineralogical composition and structure of the volcanic rocks or 
volcanoes in the neighbourhood of which they are formed. The most characteristic are 
sanidine, plagioclases, augite, hornblende, rhombic pyroxenes, olivine, and magnetite. 
Among the lapilli the most frequent are those belonging to the basaltic and andesitic 
series of rocks, especially those belonging to the vitreous varieties, and they are often 
decomposed into palagonitic matter. The pumice fragments usually present may, from 
the manner in which pumice floats, be derived from distant sources, and from the lands 
in the immediate neighbourhood of the deposit. Generally the fragments of minerals 
enumerated above are more or less enveloped by vitreous matter frequently altered by 
hydration. These points will be dealt with in greater detail when describing specially the 
rocks and minerals of marine deposits. 
The following table gives the analyses of three Volcanic Muds : — - 
Portion soluble in HCl. 
Portion insoluble in HCl. 
station. 
Depth in 
Fathoms. 
No. 
Loss on 
Ignition. 
SiOa 
AI2O3 
FejOs 
Mn02 
CaCO^ 
CaS 04 
Ca 32 P 04 
MgCOs 
Total. 
SiOa 
AI2O3 
Fe 203 
CaO 
MgO 
Total. 
VIlB. 
640 
68 
4-94 
10-76 
5-91 
7-02 
35-68 
1-05 
0-52 
2-04 
62-98 
19-17 
4-30 
5-38 
2-58 
0-65 
32-08 
VIlT. 
1750 
69 
6-30 
11-71 
5-71 
7-14 
41-43 
1-15 
g.tr. 
1-43 
68-57 
15-84 
3-71 
3-43 
1-43 
0-72 
25-13 
VIII. 
620 
70 
6-22 
16-22 
5-00 
11-69 
tr. 
32-22 
0-27 
1. tr. 
0-83 
66-23 
17-90 
4-22 
3-77 
1-44 
0-22 
27-55 
