1897] DISTRIBUTION OF PELAGIC FORAMINIFERA 25 
with only traces of carbonate of lime in its composition. Again, if 
we suppose a basin-like depression on the floor of the ocean, the 
centre of which descends to 4000 or 5000 fathoms, while the rim 
of the basin has only a depth of 1000 or 2000 fathoms, then, on 
the rim deposits of Pteropod and Globigerina Oozes will be found 
with 70 or 80 per cent. of carbonate of lime, while the centre of 
the basin will be occupied by a Red Clay with probably not a trace 
of these carbonate of lime shells. The gradual disappearance of 
these calcareous shells with increasing depth is evidently due to the 
solvent action of sea-water, and especially of deep-sea water. In 
the lesser depths a very large proportion of these surface shells 
seem to reach the bottom before they are completely dissolved, and 
accumulation takes place. With increasing depth the more delicate 
shells are dissolved before reaching the bottom, and accumulation 
becomes slower and slower, the last traces of these shells observed 
in the deposits with increasing depth being broken fragments of 
large Pulvinulinae and Sphaeroidinae. The greater quantity of lime 
in solution which Dittmar found in the Challenger samples of deep- 
sea water is apparently a consequence of the solution of the pelagic 
shells here referred to. 
During the early part of the Challenger Expedition, Wyville 
Thomson was much puzzled to account for the origin of the fine 
Red Clay which occupies the basin-like depressions of the sea-bed 
far from land, and he suggested that this was an ash! left behind 
after the solution of the carbonate of lime shells. He was led to 
this view by observing that when the shells were taken from the 
purest samples of Globigerina Ooze, and, after being carefully: 
washed with pure water, were dissolved with dilute acid, a small 
clayey residue of a red colour remained behind. I was not satisfied 
with this experiment, for I observed that the colour of the residue 
varied in different samples, and it seemed to me that the fine clayey 
matter had infiltrated the shells after they had reached the bottom. 
I accordingly collected, in the course of several months, about 10 
grammes of pelagic Foraminifera from the surface of the sea. When 
these shells were dissolved in dilute acid not a vestige of residue 
was observed. It was subsequently shown that the Red Clay came 
from a variety of sources, and that in the deep sea far from con- 
tinents it was chiefly derived from the trituration and decomposi- 
tion of floating pumice.” 
During the past year or two I have carefully collected all the 
available temperatures of the surface waters of the ocean, and from 
these have constructed a map showing the annual range of tempera- 
1 Proc. Roy. Soc., vol. xxiii., p. 45. 1874. 
2 See Murray, Proc. Roy. Soc. Edin., vol. ix., p. 247, 1876; also Murray and 
Renard, Deep-Sea Deposits Chall. Exp., p. 294. 1891. 
