284 CONVERSION OF ' GREENSTONES INTO SCHISTS. [May 1 894. 



those noticed in a former paper. 1 These green schists occupy areas 

 sufficiently considerable to require a distinctive name, and are 

 designated griine schiefer by the Swiss geologists. Commonly 

 they are in association with calc-mica schists (graue schiefer, kalJc- 

 haltig) and darkish mica-schists (thonglimmer-schiefer). My ob- 

 servations indicate the possibility that modified igneous rocks 

 may form a large part of the griine schiefer. I would not go so 

 far as to say that the whole group consists of altered igneous rocks, 

 because a tuff, or even a mud derived from a fairly basic rock, 

 might be metamorphosed into one of these green schists, and I have 

 seen some cases where the association with other schists suggested 

 such an origin ; still I am inclined to believe that the first-named 

 one is the more common. In any case, it may be useful to bear in 

 mind that slaty rocks, which look not much more altered than 

 phyllites, can be produced by pressure from igneous rocks of proper 

 constitution and texture. 



Discussion. 



Dr. C. Dr Riche Preller referred to the so-called ' Taveyanaz ' 

 sandstone of the Glarus Alps, and also to the sernifite, as rocks 

 having possibly some relation to those described by Prof. Bonney. 



The Author said that he had not had time to examine the 

 sernifite which Dr. Preller had kindly shown him, but he thought 

 it was undoubtedly a sedimentary rock, though possibly it might 

 contain comminuted igneous materials. The sandstone, he thought, 

 mnst be clastic in origin. 



1 Quart. Journ. Geol. Soc. vol. xlix. (1893) p. 94. 



