NEIGHBOURHOOD OP ST. MINVER, CORNWALL. 401 



scMstose. He regarded the scliistosity as due, in all probability, to 

 the post-Carboniferous earth-movements, which had undoubtedly 

 produced great structural and mineralogical changes in the pre- 

 granitic rocks of the west of England. He called attention to the 

 fact that many of the so-called "greenstones" of Cornwall and 

 Devon which had been described by Messrs. AUport and Phillips 

 were similar to the proterobases and epidiorites of Giimbel, and to 

 rocks from the Hartz which had been shown by Lessen to be plagio- 

 clase-augite rocks in which the augite had been partially or wholly 

 changed to hornblende by contact- or regional (pressure-) metamor- 

 phism. 



Mr. Cole agreed with the Author that these substances originally 

 contained glassy matter of a basic character, and remarked that 

 whilst the altered glass of the acid lavas had long been recognized, 

 we should have to look for the results of the alteration of the more 

 basic glass in these soft products of yellowish serpentinous matter. 



The Author, in reply, said that there was in this case no direct 

 evidence of alteration from the proximity of granite, nor from the 

 action of shearing, and he showed that in a certain instance there 

 was no displacement of a vein. There had been a disturbance 

 producing a more or less vertical squeeze. He spoke of black a& 

 well as of the green alteration-products alluded to by Mr. Cole; the 

 former would result from the separation of magnetite from these- 

 basic glasses. 



