Mr. J. S. Bowerbank on the Siliceous Bodies of the Chalk. 259 



lippine Islands by Mr. Cuming ; and I have the fac-simile of 

 Choanites Kcenigii both single and double, and of about the same 

 size as the fossil species from Wollongong near Sydney, Australia. 



The author, dismissing the evidence to be derived from the in- 

 ternal conditions of flints, then proceeds to consider their external 

 forms, and says : " And we shall find, on taking a careful review 

 of some facts of the external forms and modes in which the flints 

 are found, that the sponge theory is not only wholly unsatisfac- 

 tory, but absolutely impossible." I reply to this simply by asking 

 the author why such an origin for the chalk flints should be im- 

 possible, seeing that the author does not deny the existence of 

 other sponges of undoubted character in a silicified state ; and but 

 a few paragraphs previous to the one quoted, he describes the in- 

 vestment of Ventriculites by silex as if it were quite a natural 

 event. Now if one sponge may be thus invested and imbedded by 

 silex, why not another ? To me, the whole difierence appears to be, 

 that the one was more prone to decomposition after death than 

 the other, and therefore that we find its skeleton in a worse state 

 of preservation than in fossilized Ventriculites and Choanites. 



The author having obliged me with an inspection of the spe- 

 cimens he has figured, I may briefly say, that the supposed re- 

 volving particles in flint represented by the woodcut, page 11, 

 and for the peculiar motion of which amidst the imaginary fluid 

 flint, the author ofi'ers no principle, are in my idea merely the 

 remains of one of the large internal canals of the sponge, the na- 

 tural arrangement of the particles of which, as a matter of course, 

 presents the appearance described by the author. 



There appears to me nothing in either of the originals of 

 figures 3 and 3, Plate 1., that is in any degree anomalous. In 

 No. 2 a portion of the stem (c) has broken away from the base 

 of the Ventriculite after it had become silicified, an accident very 

 likely to happen during the subsequent elevation of the chalk, 

 and which process was probably going on during the period of 

 its deposit. No. 3 presents the imbedment of fragments, some 

 of which appear to have been shells, on the under surface of the 

 flint, the carbonate of lime having been replaced by silex ; others 

 are simply fragments of older flints. Figure 1 represents a mass 

 of flint which exhibits an appearance of having been deposited in 

 concentric layers which are exposed by what seems to have been 

 an irregular decomposition of its surface. I have often met with 

 this anomalous structure, containing the same organic remains 

 as those in the common chalk flints, but I have not yet obtained 

 a clue to the origin of its peculiar form : nor do I think Mr. 

 Smith's hypothesis of two currents in contrary directions, and 

 one whirlpool in about six superficial inches, at all likely to affbrd 

 that clue, as unluckily there are another set of contrary currents 



