412 
THE VOYAGE OF H.M.S. CHALLENGEE. 
the ten-igenous deposits, in which the materials washed down from the land play so large 
a part. The Pteropod and Globigerina Oozes of the tropical regions, being chiefly made 
up of the calcareous shells of a much larger number of tropical species, must necessarily 
accumulate at a greater ]-ate than the Globigerina Oozes in extra-tropical areas or other 
organic oozes. Diatom Ooze, being composed of both calcareous and siliceous organisms, 
has, again, a more rapid rate of deposition than the Radiolarian Ooze, while in a Eed 
Clay there is a minimum rate of growth. 
It has already been stated that cosmic spherules, sharks’ teeth, the earbones and 
other bones of Cetaceans, are much more numerous in a Red Clay than in any other 
deposit, and it has been urged that the greater or less abundance of these might be 
taken as a measure of the rate of deposition. These spherules, teeth, and bones are 
abundant in the Red Clays, because few other substances there fall to the bottom to 
cover them up, and they thus form an appreciable part of the whole deposit. In the 
organic oozes and terrigenous deposits, however, a large number of additional substances 
contribute to form the bulk of the mud or ooze, and the chance of cosmic spherules, 
sharks’ teeth, or earbones being dredged from these deposits is proportionally small, and 
as a matter of fact only a few have been obtained in these deposits. 
The volcanic materials in a Red Clay having, because of the slow accumulation, been 
for a long time exposed to the action of sea-water, are profoundly altered, the decomposi- 
tion being accomnauied by the formation of clay, massive manganese-iron nodules, and 
zeolitic crystals, just as the formation of glauconite, phosphatic, calcareous, and barium 
nodules accompany the decomposition of terrigenous rocks and minerals in deposits nearer 
continental shores. 
It has been argued by Dieulafait and others that the manganese of the manganese 
nodules has fallen from the surface and has accumulated in the red clay areas owing to 
the non-deposition of other substances. In opposition to this view it must be pointed out 
tliat .some of the Challenger’s largest hauls of manganese nodules were not in the red clay 
areas, but in Pteropod and Glol)igerina Oozes, or near volcanic cones. These Pteropod 
and Globigerina Oozes always contained a large quantity of volcanic glass, in a fine state 
of sub-division, and many minute particles of palagonite. In other Globigerina Oozes, 
where the rate of dejjosition must have been about the same or less, and where the volcanic 
particles were absent or relatively rare, only traces of manganese peroxide could be 
detected. For these reasons the abundance of manganese in a depo.sit cannot be looked 
upon as an index of the rate of deposition. The conditions in which mangane.se nodules 
ami zeolitic crystals occur, frequently suggest the proximity of volcanic phenomena at the 
bottom of the sea, and no more instructive work could be undertaken than the exhaustive 
e.xamination of one of these areas, that in the South Indian Ocean for example, where the 
surroundings suggest that the carbonate of lime shells have been removed from the deposit 
some time after deposition as a result of submarine volcajiic action. 
