TRANSITION ROCKS. 121 



tern, in order to introduce this rock in a position distinct, and very 

 distant from grauwacke. It appears to me much more simple 

 to suppose, that rocks of the same class, in different districts, 

 may present peculiar characters, than that the operations of 

 nature should have been so multiplied and complicated, as to 

 afford the endless distinctions which are thus required. In- 

 deed, I cannot help thinking, that if the Killas of Cornwall had 

 been sufficiently known, it would have excluded entirely the 

 introduction of that harsh-sounding German term Grauwacke. 

 Killas appears to me to be as proper a translation of that word 

 as Specular Iron-ore is of Eisen-Glanz, and I think may be 

 used with great propriety ; distinguishing Grauwacke and Grau- 

 wacke-slate, by Amorphous and Schistose Killas. 



The only other rock of any importance in Cornwall is Gra- 

 nite, termed Grauen by the common people, — a name also given 

 to clay-porphyry, a substance found pretty frequently in large 

 veins, (Nos. 16, to 19, 28,48.) The shades of distinction chro- 

 nicled by the mineralogist, cannot be expected to attract the at- 

 tention of the miner, who knows but two rocks, grauen and kil- 

 las, throughout the Stannaries. It has been thought that a dis- 

 tinct rock was understood by the term Elvan ; but this is a mis- 

 take, elvan may sometimes be greenstone, but in general is 

 either killas or granite, and is so termed by the miner when he 

 finds the rock harder to work in one place than in another. 



Before I entered Cornwall, I was led to believe that it 

 abounded in two kinds of granite, Primary and Secondary. 

 Never having had an opportunity of comparing them in situ, 

 I was anxious to do so here, and different localities were 

 pointed out to me ; these I examined with care, but could 

 discover no grounds to justify any distinction. Dr Berger 

 makes no mention of secondary granite ; and another gentle- 

 man, whose opinion on this, as on most subjects, will be 

 received with the utmost deference, and who had the same ob- 



Vol. VII. Q ject 



