300 Mr. Toulmin Smith on the Formation 



still clearer ; while it is that of a false theory or generalization, 

 that new facts cannot, without much distortion, be reconciled ; 

 so these phsenomena, while negativing in the most absolute 

 manner the sponge theory, beautifully illustrate the mode of 

 formation of flint which I have ventured to suggest. 



The reader must again carefully note that we are not, in truth, 

 considering the cases of sponges growing onto, attaching themselves 

 to, shells, &c. — such cases as are figured and described in Dr. 

 Johnston^s beautiful and most interesting volume. It is noto- 

 rious, and is not attempted to be denied, that we never do find 

 flints in which a root-place is visible, except in such instances as 

 I have noted on pages 4 and 9. We are considering shells scat- 

 tered on all parts of the exterior of the flints*. 



While on this point, it is proper to notice that Mr. Bowerbank 

 bases his ideas of the sponge growth of the tabular flints (Gcol. 

 Trans, vi. 184) on an entirely erroneous view of the nature of these 

 tables. They are, in fact, all made up of two distinct plates, as I 

 shall have occasion to notice hereafter f. This alone renders their 

 sponge origin quite untenable. 



It is laid down by Mr. Bowerbank on page 255, as it is by 

 Dr. Johnston (page 11), and is no doubt correct, that if one 

 sponge grow over another of different species, they never unite 

 organically; and hence he would explain the Wiltshire flints. 

 The empty space there however is too great by far for such an 

 explanation, as the parasite clings close though it does not orga- 

 nically unite. But this explanation is wholly inconsistent with 

 another very large class of facts. For it is more important to 

 observe, that, while Mr. Bowerbank is obliged in another place 

 (page 259) expressly to admit that one species of sponge was so 

 extremely diff*erent from another, that, though the inclosed spe- 

 cies is often wholly preserved, the incloser is utterly decomposed 

 (notwithstanding the " very enduring" nature of its horny ske- 

 leton), the fact is — I speak from inspection of many hundred 

 specimens in my possession — that hardly a single instance, if any 

 one, can be found in which these so diff"erent species of alleged 

 sponges have not united organically J ; insomuch that it is only 

 by artificial means that the external structure, either outside or 

 inside, of the inclosed object can be detected. One of the two 

 generalizations thus, with equal confidence, announced, must there- 



* I do not here dwell on shells inclosed in flints, as they present no diffi- 

 culty. 



t See posty p. 308. Ehrenberg, though not noticing this point, felt their 

 sponge origin untenable. See 'Ann. Nat. Hist.,* vol. ii. p. 162. 



J In a few instances small patches may be found in which they can be 

 separated, but these are extremely rare. The cause of such instances is 

 quite explicable on principles hei*eafter to be explained, which also explain 

 the Wiltshire specimens. See p. 306. 



