COLE : ON THE RED CHALK. 
37 
On the other hand, the fact remains that by far the richest 
colouring is in the lowest bed, described above, which agrees 
with the results of the a Challenger " Expedition. These 
results may possibly throw some light on the phenomenon of 
red chalk. It appears that a chalk formation is going on at 
the present time in the basin of the Atlantic, and that at a 
depth downwards from 2,300 fathoms, red clay was invariably 
found, instead of Globegerina ooze.* The Globegerina ooze 
contains some 98 per cent, of carbonate of lime, and is there- 
fore a true chalk formation. It is followed at depths varying 
from 2,100 to 2,300 fathoms by a grey ooze with less lime, 
and this in turn, at all greater depths, by red clay. 
It has been suggested that the solvent power of sea-water 
at great depths acts upon the. calcareous skeletons of 
Foraminifera, and decomposes them entirely. This accounts 
for the absence of lime, but not for the presence of the red 
colour. 
According to Mr. Murraj r ,t one of the civilian scientific 
staff of the Expedition, Manganese peroxide is abundant in 
the red clay of the Atlantic, and is a volcanic product. Sir 
Wyville Thomson % considers that the red clay of the Atlantic 
is the insoluble residue — the ash — of the calcareous organisms 
which form the Globegerina ooze, after the calcareous matter 
has been by some means removed. He describes this " ash " § 
as consisting of 1 per cent, of peroxide of iron and alumina 
and silica, left behind after removal of the lime by carbolic 
acid, with which the water is charged. 
With reference to the minerals mentioned above, as 
* The following remarks are principally suggested by the similarity of colour 
and position. Of course red chalk is not the same as red clay, but as above 
mentioned, some of the beds, notably at Warter, contain far more alumina than 
carbonate of lime. 
f Voyage of the " Challenger." Vol. i, 230. 
% Ibid., Vol. i.,229. 
§ Ibid., Vol. i., 316. 
