296 Royal Society : — 



" iiitornal oasts" to induce me to surmise that these also had been 

 originally deposited iu the chambers of Foraminit'era — their mate- 

 rial being probably very nearly the same, although its slate of 

 aggregation is ditferent. And if this was theii' real origin, 1 should 

 be disposed to extend the same view to the red clay of the ' Chal- 

 lenger ' soundings ; for a strong d priori improbability iu the sup- 

 position that this is the "ash " of the shells themselves is created 

 by the fact that wo have no knowledge (so far as 1 am aware) of 

 the presence of any such asli in calcareous organisms of similar 

 grade. It is certainly not proved by the analyses of Glohitjerina- 

 ooze quoted by Prof. Wyville Tiiomsou, since this (supposing it 

 to be free from any extraneous admixture) may ha\e contained 

 many shells partially or completely tilled with such tleposit. The 

 only analysis that could prove it would be either that of shells 

 of floating Glohijerina', which may be presumed to be alive, or of 

 those found iu the surface-layer of the Ulobiijerina-ooAd, which 

 (whether living or dead) have their chambers tilled with sarcode. 



1 submit, then, that if the red clay is (as I am disposed to be- 

 lieve) a derivative of the Glohiijerina-ooze, its production is more 

 probably due to a post mortem deposit iu the chambers of the 

 I'oraminifera thau 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 iu its character by a metamoi'phic action analogous to that 

 which changes felspar into clay. That the presence of an excess 

 of carbonic acid would have an important share iu such a metamor- 

 phosis appears from the fact, long since brought into notice by Sir 

 Charles Lyell*, of the disintegration of the granite iu Auvergne 

 and of the gneiss in the alluvial plains of the Po where subject to 

 its iutluence. 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. AVilliamsou iu 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 iu shallower waters, \\ here the same excess of 

 carbonic acid does not exist, and the aid of pressure is w anting, but 

 where a movement of water over the bottom is produced by tides 

 and currents, 1 am disposed rather to attribute the disappearance 

 of the shells to mechanical abrasion, ha\ing noticed, iu Capt. 

 kSpratt's ^i^geau dredgings, that many of the shells were worn so 

 thin that the coloured mineral deposit in their interior could be 

 seen through them — \\ hich \\ as, in fact, w liat iirst drew my atten- 

 tion to its presence. This is the explanation I should be disposed 



* Principles of Geology, 11th ed., toI. i. p. 409. 



t Memoirs of the Literary and Philosophical Society of Manchester, vol. viii. 

 p. 08. 



