Vol. 50.] CONVERSION OP ' GREENSTONES ' INTO SCHISTS. 



281 



but it occurs in rather larger flakes, and streaky patches of it are 

 more distinctly brown, which, however, may be due only to iron- 

 stains. With it a fibrous microlithic hornblende may be possibly as- 

 sociated, but the amount is not large. Many blackish granules, more 

 probably haematite than magnetite, also occur, with a somewhat 

 streaky arrangement, as if they were due to the crushing of larger 

 grains. In this slice the clear interstitial mineral is less perceptible, 

 but it contains a few rather elongated patches in which the grains 

 are larger, though generally composite. The mineral resembles 

 secondary quartz rather than secondary felspar, and in its outer 

 part is pierced by minute colourless belonites. The silica percentage 

 is found to be 61 '88, and the specific gravity is 2*72. 1 



Fig. 2. — Section cut from the middle part of the second dyke by 

 the path to the Griim Alp. 



X20. 



A. slice cut from the middle part of the third dyke shows it to be 

 not quite so markedly foliated, and the constituents, including the 

 clear interspaces, are more distinct. Of the mica a fair amount is 

 of a yellow-brown colour ; this has a tendency to occur in groups of 

 a rather tufted form. Some is greenish, and may rather be, in part 

 at least, a chlorite ; while not a little, in well-formed flakes, generally 

 smaller in size than the others, is either colourless or nearly so. 

 Dark grey sub-translucent granules (? chalybite) replace most of the 



1 I am indebted to Mr. M. W. Travers, B.Sc, University College, London, 

 for these determinations and that of the other specific gravities. 



Q. J. G. S. No. 198. v 



