106 On Transition Rocks. [Aug. 



What shall we think, then, of Mr, Allan's accuracy, when he 

 maintains that, according to the Wernerian geognosy, the granite 

 of Cornwall must be referred to the first or oldest formation, 

 because it contains tin and wolfram ? But his inaccuracies, or 

 mistatements, do not stop here. He gives it as a Wernerian 

 principle, that primitive rocks contain no mechanical deposites : 

 yet Professor Jameson, in his Elemenrs, (the work, as I said 

 before, constantly referred to by Mr. Allan), pp. 101 and 351, 

 informs us that conglomerates are found in primitive country. 

 Mr. A. asserts, also, that floetz rocks never occur in a conform- 

 able position in regard to transition strata. But how he was 

 enabled to ascertain this grand point, he has nowhere conde- 

 scended to inform us ; and yet it is very much to be desired that 

 lie had, for no such statement appears either in Professor Jame- 

 son's writings, or in any other geognostic work with which I 

 have ever met. 



The granite of Cornwall is said to have the same characters as 

 the first or oldest granite of Werner; but it would appear from 

 Mr. A.'s description of the Cornish granite that it contains J rag- 

 ■ments. Now who ever heard of fragments being found in the 

 first granite formation. Professor Jameson, from whose work 

 Mr. Allan assures us he took whatever statements he has made 

 respecting the Wernerian geognosy, distinctly mentions that 

 fragments occur only in tlie newer formation of granite, that, 

 namely, which borders on the transition rocks. It thus, then, 

 appears from Mr. Allan's own account, that the granite of Corn- 

 wall belongs to the newest, not to the oldest granite formation ; 

 and that therefore this granite is not, as he asserts, " the nucleus 

 round which Werner conceives all other rocks were deposited." 



Mr. Allan tells us that granite veins, according to the Wer- 

 nerian geognosy, occur only in such rocks as are composed of 

 the same ingredients, such as gneiss and mica-slate. But in 

 none of the books on Werner's system, in as far at least as I 

 have had an opportunity of consulting them, does any such 

 assertion appear. Besides, it is to be observed that mica-slate is 

 not composed of the same ingredients with granite ; and Pro- 

 fessor Jameson, p. 107, informs us that granite veins traverse 

 elay-slate. Is Mr. A. prepared to contend that this rock is 

 composed of the same ingredients with granite ? " The killas 

 of Cornwall," we are told, " belongs to the transition series of 

 Werner ; " and this seems to be inferred from its occurring in a 

 country said to be constructed principally of transition rocks. 

 But the killas, Mr. A. observes, assumes the appearance of 

 gneiss whenever it either approaches, or is in immediate contact 

 with, the granite. " It will be observed," says he, " by the 

 specimens from St. Michael's Mount, that the killas there 

 assumes the appearance of fine-grained gneiss." I believe most 



