2 Mr. Toulniin Smith on the Formation 



cases and to a very limited extent only, our attention will at pre- 

 sent be principally confined to the theories which attempt to 

 explain the forms and modes in which the flint is now found. 



Of these, the theory of Dr. Buckland, that flint and chalk 

 being deposited together in the form of viscid fluids the former 

 separated itself from the latter according to the well-known laws 

 of chemical affinity, is of too indefinite and general a character to 

 be readily applied and tested in individual cases, though, as we 

 shall find, such opportunity does sometimes occur. The theory 

 of Mr. Bowerbank alone proposes a distinct and definite explana- 

 tion of all the forms and modes in which flint, either in nodules 

 or tabular masses, is actually found. To that theory therefore 

 I will direct chief attention, the more so as it has very recently 

 been advocated in this Journal*, and as I believe the views ex- 

 pressed in Mr. Bowerbank^s published paper on the subjectf are 

 still held by their author, and they come from him with an au- 

 thority so great as to claim the most careful and candid exami- 

 nation. 



Mr. Bowerbank's views may be shortly stated to be, in his 

 own words, " that the common tuberous flints, the horizontal 

 tabular flints, and those forming perpendicular or oblique veins, 

 were all produced by the same agency,^^ namely, in all cases 

 from sponges, of which those flints occupy the exact places, 

 though of the sponges themselves but small remains generally 

 exist (see pp. 183 and 186 of the paper referred to). 



It is not my intention to dispute the particular facts stated by 

 Mr. Bowerbank as applying to the cases observed by him. What 

 I undertake to show is that those, admitting their correctness, 

 are not all the facts, and that many others exist wholly incon- 

 sistent with the conclusions which Mr. Bowerbank would draw. 

 And it is here well deserving of remark, that, while Mr. Bower- 

 bank finds in such abundance on the exterior of all flints sponge 

 spiculse and evidence of the mouths of the excurrent canals of 

 sponges, Ehrenberg finds the same exteriors to consist almost 

 entirely of the skeletons of Infusoria ! No one accustomed to 

 the use of the microscope can be otherwise than aware how much 

 very minute objects seen under a high power are apt to assume 

 a character in accordance with preconceived notions ; and when 

 we find such careful observers as Mr. Bowerbank and Ehrenberg 

 thus difiering altogether and in so very marked a manner in the 

 results of their examinations, it may be allowed us, in all humi- 

 lity, to call in the aid of other classes of facts to clear up the 

 mystery, and this I now proceed to do. 



I fully admit that spiculse are not uncommonly found in some 



* By Prof. Ansted, 1844. f Geol. Trans, vol. vi. 181. 



