1814.] nn Tiwiskion Hocks. 115 



little more consideration : he may be assured I never will inten- 

 tionally misstate any fact, and I am not very likely to voliinteor my 

 opinion on a subject I do not comprehend. ,<;fh.'<j 



Allow me again to thank yOu for the confirmation you have 

 aflbrded my observations, with regard to the granite and killas of 

 Cornwall. 



Vou have acknowledged that you found granite veins proceeding 

 from the little hill of St. JNIicliael's Mount into the clay slate which 

 rests upon that granite ; you found in these veins fragments of the 

 clay slate. You allow that they are true veins ; and you yet venture 

 to consider them as the oifspridg of deposition. You talk of beds 

 which occur at the west side of tlie Mount,* and you call it iu 

 consequence transition granite. But why do you, towards the end 

 of your paper, call the gratiite of Cornwall primitive granite? Did 

 you find any distinction between that of the Mount and that of 

 Dartmoor? and does not tin occur in veins in both ?t And with 

 respect to killas, you declare tiiat substance to be the same with 

 transition slate ; and as i\Ir. Jameson recognises no transition slate, 

 except grauwacke slate or flinty slate, I consider you have made out 

 my case as completely as if you had gone to Cornwall for the 

 purpose. Grauwacke, I have already stated, I found in the most 

 unquestionable shape in different parts of Cornwall ; at Grampound 

 you foimd it alternating with grauwacke-slate ; and, lately, I was 

 presented by Mr. Buckland, of Oxford, with a specimen from the 

 vicinity of Probus, as highly characterised as any grauwacke from 

 the neighbourhood of Moffat, where 1 was first taught by Professor 

 Jameson what that rock was. 



I shall now finish this long letter, by Informing you, with recard 

 to the age of tin and wolfram, that 1 have great reason to suspect 

 they are found in no other granite but that of the oldest formation.^ 



* I dill examine all sides of tlie Mount ; and I must confesf, tluit I found no 



appearance whatever that conveyed to tnc thesiiiailc!-! notion of ;i bed of granite. 



[The examination, in that case, must have been but carelesily made; for the 

 j;rani(e beds arc very conspicuous at low water, and may be easily traced a con- 

 siderable way. — T.] 



+ I did not particularly examine the granite of Uartmoor ; but there is &, 

 striking Hillercncc between the sranile of St. Jhlichael's Mount and that of the 

 penin?ula of I'enzance; but hati ihey been perfectly similar it would not liave 

 altered my opinion. The terms piimitiiie and /laiisilivn allude only to position, ami 

 this can be determined only by examination. When I find granite l>ing over 

 traiiiilion ihlc, 1 call it liunsilion granite. If I find its characters not to a^rec 

 with those of Werner's liiinsition granite, I conclude that Werner's induction was 

 imperfcci, and that his opinions on the subject are incorrect. At the same lime it 

 i» by no means doing justice lo Werner to compare the opinions which he enfei'- 

 laiiied l;j \ears ago with our present knowledge. Tiiis is wliat Mr. Allan does', 

 lie cannot know Werner's present opinions till he publish his system, 1 have beeu 

 told (hat this is his inleiilion. — T, 



i This o])inion, lor any thing that I know to the contrary, may be correct, 

 riie granite and the stale in wiiirli the tin veins of Cornnall occur [ called primi- 

 liK' in my paper on ihe subjecl. because I saw no proof of (heir being tinnsitioR. 

 Hill if lin veins were lo be found in Si. iMicliael'!, Mount, I should consider (his as 

 a !iiflirienl proof that they occur alio in iransition foruiations,— T. 



U 'J 



