1S13.] 



Transition Rocks of Werner, 



425 



witnessed at any time, either in the neighbourhood of Coniston,* 

 or on the right bank of the Blackwater, a little below Fermoy, 

 in the county of Cork. The formation of this class of rocks was 

 therefore subsequent to the formation of living animals, whose 

 existence is supposed to be proved by the occurrence of organic 

 remains in the composition of the rock. 



In Cornwall, in Westmoreiand, in Galloway, and in the 

 counties of Down and Derry, this rock lies directly on granite, 

 — a circumstance which we should at first sight be inclined to 

 consider as indicating its subsequent formation. This thought, 

 however, vanishes the moment we contemplate the veins of 

 granite by which it is traversed. Of these there are many ex- 

 amples ; but the most striking are at the Louran in Galloway, 

 and at St. Michael's mount in Cornwall. 



It is many years since Sir James Hall laid before this Society 

 an account of his observations on the granite district of Gallo- 

 way, of which the Louran forms a part; and to the persevering 

 activity of that gentleman we are indebted for the display of 

 one of the most interesting exhibitions of granite veins that 

 exists. The peculiarities observable in Galloway were first 

 pointed out to me by him ; and as he has so lately favoured the 

 Society with a particular account of them, it leaves me nothing 

 to say regarding that quarter. 



At St. Michael's mount the shooting of the veins from the 

 great mass of granite is also most strikingly exemplified. They 

 were here first noticed by Professor Playfair, who compares 

 them, most aptly, to the ramifications of the vegetable root;t 

 for, indeed, nothing can be more illustrative of the phenomenon 

 as it is here exhibited- 



It is to be observed that granite veins, particularly when ex- 

 tremely minute, usually differ in texture from the mass to which 

 they belong. While the little peak of St. Michael's Mount 

 maintains a similarity of character with all the rest of the Cor- 

 nish granite, not only in point of internal structure, but with 

 respect to the tin and copper veins which traverse it, as well as 

 by the massive blocks, hewn by the corroding hand of time, 

 which ornament its summit ; the veins that set off from it gra- 

 dually become finer as they recede, but still preserve the perfect 

 character of the rock. The importance deservedly attached by 

 Dr. Hutton to the phenomena of granite veins, gave rise to a 

 variety of hypotheses among those who were inclined to consider 

 this rock as the original deposite, who have accounted for their 

 formation in different ways. 



* * Since I read this paper, I wrote to a friend at Conisfon, requesting a few 

 of these specimens, well characterised, might be sent me : some of which are 

 deposited, alonjo- with the rest, in the cabinet of the Society, 

 t Illustrations of the Huttonian Theory, p. 318, 



