296 Royal Society :-— 
“internal casts” to induce me to surmise that these also had been 
originally deposited in the chambers of Foraminifera—their mate- 
rial bemg probably very nearly the same, although its state of 
aggregation is different. And if this was their real origin, I should 
be disposed to extend the same view to the red clay of the ‘ Chal- 
lenger’ soundings ; for a strong @ priori improbability in the sup- 
position that this is the ‘ash ” of the shells themselves is created 
by the fact that we have no knowledge (so far as I am aware) of 
the presence of any such ash in calcareous organisms of similar 
grade. It is certainly not proved by the analyses of G'lobigerina- 
ooze quoted by Prof. Wyville Thomson, since this (supposing it 
to be free from any extraneous admixture) may have contained 
many shells partially or completely filled with such deposit. The 
only analysis that could prove it would be either that of shells 
of floating Globigerine, which may be presumed to be alive, or of 
those found in the surface-layer of the Globigerina-ooze, which 
(whether living or dead) have their chambers filled with sarcode. 
I submit, then, that if the red clay is (as I am disposed to be- 
lieve) a derivative of the Globigerina-ooze, its production is more 
probably due to a post mortem deposit in the chambers of the 
Foraminifera than to the appropriation of its material by the living 
animals in the formation of their shells. That deposit may have 
had the character, in the first instance, of either the green or the 
ochreous silicate of alumina and iron, which constitutes the 
material of the internal casts, and may have been subsequently 
changed in its character by a metamorphic action analogous to that 
which changes felspar into clay. That the presence of an excess 
of carbonic acid would have an important share in such a metamor- 
phosis appears from the fact, long since brought into notice by Sir 
Charles Lyell*, of the disintegration of the granite in Auvergne 
and of the gneiss in the alluvial plains of the Po where subject to 
its influence. And the same agency (especially when operating 
under great pressure) would be fully competent to effect the re- 
moval of the calcareous shells, as was distinctly pointed out nearly 
thirty years ago by Prof. W. C. Williamson in his classical memoir 
on the Microscopic Organisms of the Levant Mudt. This seems 
to me the most probable mode of accounting for their disappear- 
ance from a deep-sea deposit, where no mechanical cause can be 
invoked. But in shallower waters, where the same excess of 
carbonic acid does not exist, and the aid of pressure is wanting, but 
where a movement of water over the bottom is produced by tides 
and currents, I am disposed rather to attribute the disappearance 
of the shells to mechanical abrasion, having noticed, in Capt. 
Spratt’s Augean dredgings, that many of the shells were worn so 
thin that the colovred mineral deposit in their interior could be 
seen through them—which was, in fact, what first drew my atten- 
tion to its presence. This is the explanation I should be disposed 
* Principles of Geology, 11th ed., vol. i. p. 409. 
Bethea of the Literary and Philosophical Society of Manchester, vol. viii. 
p. 98. 
