of the Flints of the Upper Chalk. 8' 



flints, but they are most assuredly not always found ; in some 

 flints they are very numerous, while in others from the same spot 

 they are exceedingly rare, arfd in very many wholly wanting. 

 Now these sponge spiculse are indestructible. The destruction 

 of the structure of the sponge, which this theory requires as a 

 necessary postulate, would not destroy them. How then is it 

 that they are thus variably present ? And it is important to re- 

 member that similar spiculae are also found in the chalk itself. 



It may be remarked, in passing, that this theory, if true, pre- 

 sents us with a y)h3enomenon still more extraordinary and unac- 

 countable than that which it is called in to explain. It is taken 

 for granted that the flint itself is a foreign substance which has 

 filled the places formerly occupied by sponges. Now how hap- 

 pens it that flint should be found in such places only ? and this 

 restriction, be it observed, besides being expressly made by Mr. 

 Bowerbank, is necessary to the existence, in any shape, of the 

 theory. If it is once admitted that flint is ever, or may be even 

 in a single instance, found elsewhere, the theory ceases to be an 

 explanation of the phsenomena, and becomes of no value to the 

 philosophical inquirer. Now, can it be shown that silex has any 

 peculiar aflinity for either the animal substance or the horny 

 skeleton of sponges ? The contrary is known, as matter of fact, 

 to be the case. Facts palseontological as well as recent might be 

 cited in abundance in disproof of this necessary postulate of the 

 sponge theory. I have undoubted sponges in my possession 

 from the chalk, w^hich, instead of being wholly silicified, are in 

 part so, and in part still in the chalk, while the flint is otherwise 

 extended beyond the boundary of the sponge. Such facts dis- 

 prove the alleged special aflinity. But if we turn to events going 

 on before our eyes, we find that not only is silex abundantly se- 

 creted on the leaves and stalks of the Plumbago, and at the joints 

 of the bamboo, and in many other instances, but the plants grow- 

 ing near the Geysers in Iceland, as well as near the hot springs 

 in some of the Azores, are incrusted with silex, in which many 

 are completely imbedded, and that without the presence or neigh- 

 bourhood of any sponge whatever. These facts alone, apart from 

 those of a like nature which will presently be named, and which 

 every one must feel to be clearly analogous, are fatal to the 

 theory. They show analogous results produced at the present 

 day by a wholly different set of causes from those suggested by 

 the sponge theory and necessary to its maintenance. 



It is admitted that it is very rarely, if ever, that the reticulated 

 tissue which is conceived to have belonged to sponges is found 

 throughout any considerable portion of the flint ; that often but 

 little of such tissue is found ; often no trace of it at all. Now 

 these facts want, but have not had^ explanation. How is it that 



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