406 APPENDIX. 



is from the very paper in whicli he announces his hypothesis. In 

 that paper he mentions that the consohclation of all the hard crust 

 of the globe has been effected by lieat and fusion^ extending it to 

 secondary as well as primitive rocks, and mentioning particularly 

 Spanish marble, shell limestone, oolite, and chalk. 



"This operation of heat, he says, is exemplified by cliallc^ which 

 is to he found in all gradations^ from Tnarhle to loose chalk. This is 

 his precise notion, but not his words. I had once looked at this 

 paper before, and thought much of this theory ; but this thought 

 had been obliterated from my mind by thoughts advanced by 

 others, as I thought in consistency with the sentence I quoted 

 from Bakewell. At least, one objection to Hutton's views would 

 be removed by modifying his theory in the manner it seems to 

 be by Bakewell. Though Hutton does not think this to be ne- 

 cessary ; for he appears to feel no difficulty in accounting for 

 petrifactions of wood on his hypothesis, for he mentions that tue 

 have many proofs of the penetration of flinty matter, in a state of fusion, 

 in other bodies, such as insulated j^ieces of flint in chalk or sand, and 

 fossil xvood penetrated ivith silicious matter. 



" Still, the grand reasons of Hutton for employing heat as the 

 agent of consolidation are opposed to the above modification of 

 his theory. These reasons, as you know, are the insolubility of 

 most mineral substances in water, and the disappearance of the 

 water from the cavities of minerals which have been consolidated. 

 The first is, indeed, the great one for Hutton; for the crystalliza- 

 tion of salts in water, and tlie existence of liquids, in some cases, 

 in the cavities of the most solid minerals, show well enough that 

 the water might or might not disappear, as the circumstances 

 were different. 



" If the Huttonians maintain, as he did, the formation of petri- 

 factions by heat, which consistency requires, I concede, indeed, to 

 you that that fossil-tree stands as a grand monument of some dif- 

 ferent process ; and yet, we can hardly suppose that they do not 

 see great difficulty in the common notion on the subject. The 

 rapidity with which the petrifactions must have taken place — a 

 point well illustrated in Hayden's Geological .Essays — seems to 

 require some new notions on the subject. What these may be, 

 1 cannot tell ; but I believe that neither of these two hypotheses 

 will be adopted exclusively, half a century hence, on this point, 



