REPORT ON THE DEEP-SEA DEPOSITS. 
241 
they pass insensibly into Blue and Green Muds, in others into Coral Muds and Sands, 
or with increasing depth into Globigerina, Pteropod, and Diatom Oozes or Red Clays — 
their chief characteristic being the relative abundance of volcanic materials. 
Volcanic Muds . — There are 38 examples of Volcanic Muds among tho Challenger 
soundings and dredgings, described in the Tables of Chapter II. In depth these range 
from 260 to 2800 fathoms, the average depth being 1033 fathoms. Of these — 
9 are under 500 fathoms. 
13 „ from 500 to 1000 ,, 
7 „ „ 1000 „ 1500 
3 „ „ 1500 „ 2000 
2 „ „ 2000 ,, 2500 
4 „ over 2500 „ 
The colour of these deposits was in the majority of cases brown or grey. In 
depths between 2000 and 2800 fathoms there was only a trace of carbonate of lime, but 
in one sample from 260 fathoms there was 56‘59 per cent., the average percentage in 
these Volcanic Muds being 20'49. Arranged in groups of 500 fathoms, the mean per- 
centages of carbonate of lime are as follows 
In less than 500 fathoms. 
From 500 to 1000 ,, 
„ 1000 „ 1500 
„ 1500 „ 2000 
„ 2000 „ 2500 
Over 2500 ,, 
24;69 average per cent. CaCOg. 
26-04 
20-34 
3 ? 
31-30 
33 
trace. 
trace.. 
The carbonate of lime derived from pelagic Foraminifera is in some cases as high as 
35 per cent., the average being 10*50 per cent. ; that from bottom-living Foraminifera 
ranges as high as 10 per cent., the average being 2-82 per cent. ; that from the remains 
of other organisms ranges to 21-59 per cent., and averages 7*17 per cent. 
The amount of residue varies from 43 "41 to nearly 100 per cent., averaging 79-51 
per cent., and is usually brown or black. The siliceous organisms range from 1 to 5 per 
cent., the average being 1-82 per cent., and consist of Radiolaria, Sponge spicules, 
Diatoms, and arenaceous Foraminifera. True glauconitic casts or characteristic glauconitic- 
grains have not been observed in typical Volcanic Muds. 
The mineral particles make up from 5 to 75 per cent, of the whole deposit, the 
average being 40-82 per cent. The particles are nearly always angular, and have a mean 
diameter of 0-11 mm., the range being from 0-06 to 0-20 mm. Quartz is mentioned only 
once and glauconite twice, but, as above stated, typical glauconite grains may be said to 
be absent. 
(deep-sea deposits chall. exp. — 1891.) 
31 
