of the Flints of the Upper Chalk, 805 



nodules never were sponges. For I am prepared to demonstrate 

 to any one who will favour my cabinet with an inspection, that 

 the Ventriculites thus invested as to their roots were not dis-" 

 ruptedj but, on the contrary, were growing normally and in situ 

 when invested by the flint : and the great specific gravity of the 

 flint readily accounts for its sinking into the soft mud so as thus 

 to invest their roots. It is further obvious, that had they been, 

 as alleged, disrupted and lying on their sides, the accumulations 

 of flint would be all on one side, they forming merely the attach- 

 ments of the sponge ; whereas the fact is, that the general rule 

 is a pretty equal distribution of flint all round. If a special 

 mass lies on one side, it is capable of explanation. 



My space warns me that I must hasten to notice the explana- 

 tions attempted of the figured specimens. 



Mr. Bowerbank would have us believe (page 257) that the 

 woodcut (page 11) is explained by the flint being "the remains 

 of one of the large internal canals of the sponge.^' When the 

 reader is reminded that this is an assumption of a petrified mass 

 of revolving water (revolving, too, normally, after all the rest of 

 the sponge has utterly decayed), it cannot be necessary to notice 

 the suggestion further. 



I noticed Mr. Charlesworth^s silicified pulp-cavity with a reser- 

 vation. I have seen the specimen. There are undoubted poly- 

 thalamia in it, though not such apparent sponge tissue. For the 

 reasons named in my former paper, I see no difficulty in account- 

 ing for the presence of the minute polythalamia, though very 

 great in imagining the growth of any sponge in such a locality. 

 As to my own figured specimen of jaw, I certainly was not then, 

 nor am I now, aware that the substance of the teeth and jaw is 

 silicified, but know the reverse to be the fact ; and when the 

 reader learns that the teeth in that specimen are anchylosed to 

 the jaw, which is solid below them, he will feel that no " space 

 intervening between the tooth and its socket ^^ ever existed. But 

 Mr. Bowerbank's attempts to explain figures 1, 2 and 3 are the 

 most extraordinary. The condition of figure 2 is so fully ex- 

 plained in my former paper as at once to refute the notion of an 

 '' accident during the elevation of the chalk,^^ — a notion under any 

 circumstances so far-fetched and, on every ground, inadmissible, 

 that it cannot be necessary to combat it. Mr. Bowerbank can- 

 not, however, have read the description of this specimen. As to 

 fig. 3, of which it is most gratuitously said (page 259) that some 

 of the fragments " appear to have been shells,^' in direct oppo- 

 sition to the fact, Mr. Bowerbank is compelled to admit that the 

 fragments are "fragments of older flints,^^ which is just what 

 the specimen was engraved to show, and which Mr. Bowerbank 

 leaves wholly unexplained. As to figure 1, 1 cannot at all under- 



