Vol. 54.] 



SCHISTS OF THE ST. GOTHARD PASS. 



367 



of the crystal (see fig. 6, below). Occasionally we find that an end 

 or a small portion of a hornblende-crystal is apparently replaced by 

 these flakes.^ Sometimes also a separate grain of hornblende may be 

 found, rather prismatic in outline, which seems to form a nucleus 

 to three or four flakes of biotite and presents, if I may so express it , 

 a residual aspect. 



Fig. 6. — One end of a lancet-sliaped crystal of actinolite, tipped and 

 fringed ivith fialces of hiotite. (From the ascent to the St. Gothard 

 Pass.) 



X25. 

 [a = actinolite ; b = biotite.] 



(6) Chlorite. This mineral has a more or less fan-like growth, 

 is fairly pleochroic, changing from a light tawny buff to a rather 

 pale dull green, exhibiting low polarization-tints and straight 

 extinction. It is abundant only in one slice. Here it occurs in 

 somewhat irregular patches, which, however, in one or two cases 

 are seen to be associated with hornblende, and led me to infer that 

 the mineral has replaced biotite. 



(7) Epidote, not unfrequent in grains and rather irregular 

 prisms, having the usual aspect and tints, without and with the 

 polariscope, though this instrument shows that low-coloured grains 

 sometimes occur with the others, and the possibility that certain of 

 these may be zoisite is suggested.^ 



^ As if (to use a simile) the design of a hornblende-building had been carried 

 out with biotitic materials. 



^ They do not generallj^ admit of accurate measurements. 



Q. J. G. S. No. 215. 2d 



