232 
THE VOYAGE OF H.M.S. CHALLENGER. 
It will be noticed that the fine washings increase with the depth, while the abundance 
of mineral particles and their mean diameter are irregular, though on the whole they 
diminish in size and abundance with greater depth and greater distance from land, where 
the sea is not afiected by floating ice. It must be noticed also that in the neighbour- 
hootl of some continental shores, where there are many volcanic rocks, the deposits are 
made up to a great extent of the disintegrated parts of these rocks, and thus cannot be 
distinguished from the Volcanic Muds formed around volcanic islands.^ 
The following table shows the average composition of the Challenger samples of 
Blue ]\Iud, and it will lie seen that, compared with the similar table for Ked Clay, the 
percentage of minerals is much higher and the fine washings less abundant 
: — 
1 
r Pelagic Foraminifera, . 
7-52 
Carbonate of lime, < 
Bottom-living Foraminifera, . 
1-75 
1 
[ Other organisms, 
3-21 
12-48 
1 
( Siliceous organisms, 
3-27 
Residue, . . ^ 
Minerals, 
. 22-48 
1 
[Fine washings, 
. 61-77 
87-52 
100-00 
The following are analyses of two samples of Blue Mud, one from the Pacific, the 
other from the Atlantic : — 
' 
POimoX SOLUBLE IN 
HCI. 
Portion insoluble in HCI. 
_o 
5 
r. 
Doiitli in 
Fathoms. 
No. 
I Loss on 
1 Ignition. 
OJ 
p 
AI..O 3 
FC3O3 
MnO. 
CaCOa 
CaSOj 
Ca- 32 POj 
MgCOa 
Total. 
SiO.. 
AI 0 O 3 
FeoOa 
CaO 
MgO 
Total. 
■•213 
1 
2050 
63 
4-92 23 •52 
: 
775 
7-50 
g. tr. 
1-75 
0-68 
tr. 
1-14 
42-24 
39-84 
7-33 
3-73 
1-63 
0-31 
52-84 
I3-23 
j 
1900 
04 
5-0O : 28-20 
5-50 
5-61 
2-94 
0-42 
1-39 
0-76 
44-82 
36-00 
8-05 
2-77 
2-51 
0-25 
49-58 
No. 63 Ls of niau-rial obtained from the trawl, No. 64 from tow-net at trawl. 
These two analyses show a striking difference when compared with those of jielagic 
deposits. The quantity of insoluble residue is much greater than the average in deposits 
from similar depths further removed from land, for it will be seen that it makes up in 
these two wises about one-half of the deposits. This indicates a higher percentage of 
mineral jairticles not decomposaljle by hydrochloric acid, and may be attributed to the 
presence of the minerals and rocks from continental lands, in which quartz plays the 
most important part, thus being in accord with what we have just said as to the origin of 
this deposit. In the portion soluble in acid we have the hydrated silicate of alumina and 
ferric oxide, but in these two analyses the percentages of these substances are less than 
> See PI. XI. fiK'. 2 ; PI. XXVII. fig. 4. 
