570 Transactions of the Societij. 



spicula ; neither can any connection be determined between the 

 position of penetrating tubules and the size, shape, and distribution 

 of the pretty conoidal enlargements. 



Examination of deep-sea soundings, given to me by Dr. 

 Wallich, F.L.S., and by H. T. Whittell, Esq., one of the Fellows 

 of this Society, from the Atlantic and South Pacific, from depths 

 as great as 2000 fathoms, show sponge spicula with perforations 

 and enlarged axial canals, but none of the extraordinary shapes are 

 present. The. vast pressure to which the spicula were exposed as 

 they travelled along the sea floor to their resting-place, is the only 

 additional cause which can be associated with the occurrence of the 

 unusual forms of the axial canal ; but the modus operandi does not 

 appear. 



During the progress of these investigations I have been struck 

 with the fact that, whilst erosion of the spicula has gone on greatly 

 within, the most delicate spinules of the outside coat of silica are 

 intact. In the same deposit, however, there are worm-eaten-looking 

 spicula, as has already been mentioned, and some spicula which, 

 with enlargement of the axial canal, present irregular scalings off 

 of layers of the sihceous outer covering (Fig. 15), but the cause of 

 the one is evidently connected with vegetable organisms, and that 

 of the other does not appear clear. 



It appears that time has something to do with the amount 

 of solution, and that the erosive action of the Thallophyte is 

 more rapid than that of the pressure and chemical action of the 

 sea itself. One cannot but 1)6 struck with the evidences of the 

 solution of organic silica which is proceeding on the floor of the 

 sea as well as at the surface. The sponge spicule and the Eadio- 

 larian of the deep ooze are eroded and wasted in the same degree as 

 the Diatomaceae of the surface. The causes may be partly different, 

 but biological energies influence the solution on the whole more 

 than the physico-chemical. 



The biological cause has been noticed in this communication in 

 relation to the spicula found at great depth, and Mr. Carter has 

 connected it with common sponge life ; but what the physico- 

 chemical action may be is a matter which requires careful con- 

 sideration. 



Of course the explanation at hand is pressure and carbon 

 dioxide held in suspension in sea water. That the pressure is 

 enormous at even moderate depths is true, and it is equally certain 

 that pressure assists the dissolving or combining power of carbonic 

 acid gas. But is there any free carbonic acid gas in the sea ? 



What deep-sea deposits I have seen (thanks to the kindness of 

 members of this Society), calcareous and siliceous, or both, in 

 their nature, do not carry conviction to my mind that they have 

 been subject to erosion under the influence of free carbonic acid gas, 



