201 METAMORPHOSED ROCKS OF THE START AREA. [vol. Ixxix, 



occurs in the form of schists, the pillow-lavas having been con- 

 verted into actinolite-chlorite-epidote-albite-schists of a general 

 green colour. These very frequently contain biotite. and were 

 metamorphosed by the Bodmin-Moor granite, but otherwise 

 resemble the Green Schists of the Start area. 



In several parts of Cornwall and Devon powerful overthrusts 

 had repeated the normal succession, and these appear to have been 

 influenced by the resistant granite-masses. The period of over- 

 thrusting is post-Carboniferous, and may be later than the in- 

 trusion of the granite. The speaker enquired whether the Author 

 considered that the Start Schists had also been overthrust, and, if 

 so, at what period. He also asked when the quartz-albite veins 

 had invaded the Devonian sediments north of the Start Schists. 



Dr. G. H. Plymen remarked on the close resemblance of the 

 hornblende-epidote-albite-schists to the schists of Sark. Prof. 

 Bonney & the Rev. E. Hill had noted the practical absence of 

 olivine-bearing rocks in Sark, although Sark is otherwise com- 

 parable to the Lizard area, and the Author's suggested relation of 

 the Start Schists with olivine-basalts was interesting. 



The intrusion of quartz-albite veins into the Devonian rocks 

 seemed to suggest post-Devonian metamorphism. If the Author 

 had reason to hold this opinion, it might have important bearing 

 on the period of metamorphism in the Channel Islands, especially 

 as no metamorphic rocks were at present known in the basement 

 Cambrian conglomerate of either Jersey or Alderney. 



The Author thanked the Fellows for their kind reception of 

 his paper. In reply to Mr. Dewey, he stated that he felt that the 

 exact nature of the movement along the metamorphic boundary, 

 whether overthrusting or normal faulting, was still an open question. 

 The boundary evidence, so far as he was able to interpret it, did 

 not support the view of overthrusting. The point raised by 

 Dr. Plymen was of considerable interest. 



The albite- and quartz-albite-veins in the Devonian sediments 

 lying north of the Start Schists were, in his opinion, attributable 

 to circulating solutions during the Armorican folding movement in 

 which the Devonian rocks were involved, the albite being drawn 

 from the Green Schists immediately to the south. He was of 

 opinion that this movement, while possibly giving rise to more 

 complicated mechanical structures in the Start Schists, effected 

 but little mineralogical change within them. 



