REPORT ON THE DEEP-SEA DEPOSITS. 
231 
residue is 87 ‘52, and the range with respect to depth is the reverse of that given for the 
carbonate of lime. 
With reference to the siliceous organisms in the Blue Muds, these are estimated in 
the Tables as ranging from 1 per cent, in several instances to 15 per cent, in two cases, 
the average for the whole being 3 ’27 per cent. These organic remains consist of the 
frustules of Diatoms, Radiolarians, Sponge spicules, arenaceous Foraminifera, and casts of 
the carbonate of lime organisms in glauconite or some allied silicate. 
The mineral particles are mostly derived from the adjacent lands, and consist largely 
of the fragments and minerals of the various rocks forming the continents. The size of 
the mineral and rock particles varies much with the position ; they are as a rule larger 
near the shore, and smaller as the deep sea is approached, except in those regions 
affected by floating ice. More than half of the deposit is in many cases made up of the 
mineral particles, consisting largely of rounded grains of quartz. 
In the Challenger samples the mineral particles are stated to be angular in 32 cases, 
rounded in 3 cases, and in 21 cases to be angular and rounded. The size varies from 
0'06 to 0’30 mm. in diameter, and the average diameter is 0'115 mm. The percentage 
is very variable, ranging from 1 per cent, in several cases to 75 per cent, in one 
instance, the mean percentage being 22*48. 
It may be noticed here that quartz particles, which are relatively rare, not discernible, 
or absent in typical pelagic deposits, are the most abundant among the mineral particles of 
these terrigenous deposits, which are further characterised by the presence of particles of 
older crystalline or schisto-crystalline rocks, quartzite, sandstones, limestones. Among the 
minerals we observe, besides quartz, orthoclase and plagioclase, green hornblende, augite, 
white and black mica, epidote, chloritic scales, zircon, tourmaline, &c. Glauconite cannot 
be considered characteristic of Blue Muds, but is to be found in nearly all of them, 
though in limited quantity compared with what is met with in those other terrigenous 
deposits called Green Muds. 
The fine washings range from 16*11 per cent, to 97*00 per cent., the average being 
61*77 per cent. The fine washings in the Blue Muds are probably always less abundant 
than in the Red Clays and Radiolarian Oozes. 
The following table is arranged to show the average percentage of the minerals and 
fine washings, as also the average size of the mineral particles, for successive groups of 
500 fathoms : — 
Under 500 fathoms, 
Minerals. 
29-08 
Size. 
0-137 mm. 
Fine Washings. 
53-22 
500 to 1000 
30-18 
0-102 „ 
56-48 
1000 „ 1500 
19-77 
0-118 „ 
58-29 
1500 „ 2000 
23-33 
0-115 „ 
62-25 
2000 „ 2500 
18-00 
0-119 „ 
66-23 
Over 2500 „ 
16-89 
0-087 „ 
69-46 
