CHAP. IIL] TENERIFFE TO SOMBRERO. 217 
The larger foraminifera are attacked, and instead of being viv- 
idly white and delicately sculptured, they become brown and 
worn, and finally they break up, each according to its fashion : 
the chamber-walls of Globigerina fall into wedge-shaped pieces, 
which quickly disappear; and a thick rough crust breaks away 
from the surface of Orbulina, leaving a thin inner sphere, at 
first beautifully transparent, but soon becoming opaque and 
crumbling away. 
In the mean time, the proportion of the amorphous red 
clay to the calcareous elements of all kinds increases, until the 
latter disappear, with the exception of a few scattered shells of 
the larger foraminifera, which are still found, even in the most 
characteristic samples of the red clay. 
There seems to be no room left for doubt that the red clay 
is essentially the insoluble residue, the ash, as it were, of the 
ealeareous organisms which form the globigerina ooze after 
the calcareous matter has been by some means removed. An 
ordinary mixture of calcareous foraminifera with the shells of 
pteropods, forming a fair sample of globigerina ooze from 
near St. Thomas, was carefully washed, and subjected, by Mr. 
Buchanan, to the action of weak acid; and he found that there 
remained, after the carbonate of lime had been removed, about 
one per cent. of a reddish mud, consisting of silica, alumina, 
and the red oxide of iron. This experiment has been frequent- 
ly repeated with different samples of globigerina ooze, and 
always with the result that a small proportion of a red sedi- 
ment remains, which possesses all the characters of the red 
clay. I do not for a moment contend that the material of the 
red clay exists in the form of the silicate of alumina and 
the peroxide of iron in the shells of living foraminifera and 
pteropods, or in the hard parts of animals of other classes. 
That certain inorganic salts other than the salts of lime exist in 
all animal tissues, soft and hard, in a certain proportion, is un- 
doubted ; and I hazard the speculation that during the decom- 
