﻿710 PROF. T. G. BONNEY AND MISS C. RAISIN ON THE [Nov. 1905, 



though favourable to the production of higher tints, do not appear to 

 be the only factors. Extinction is generally straight. 



The slabby serpentine from the Gorner Grat has been so fully 

 described, 1 that we need only repeat that it is a felted foliated mass 

 of rather minute minerals like those already described, the highest 

 polarization-tints being the clear yellow of the first order. The 

 author then (1890) suggested the possibility that part at least might 

 be antigorite, and would now identify it without hesitation, for a 

 very faint pleochroism is occasionally perceptible. 



Pig. 2.— Slaty serpentine from the Gorner Grat, sliced generally 

 parallel with the micro foliation. [Magnified 50 diameters.'] 



[Geol. Mag. 1890, p. 537. We are indebted to the Editor, 

 Dr. Henry Woodward, P.R.S., for the use of the block.] 



As the augitic serpentine of the Rinelhorn is very abundant in 

 that neighbourhood we should naturally suppose those slaty ser- 

 pentines on the Gorner Grat to be modifications of it. 2 But one of 

 us accidentally discovered the need of caution. Probably on his 

 third visit (in 1860), certainly some years before he collected rocks 



1 Geol. Mag. 1890, p. 533. Miss Raisin has specimens (not quite so slabby) 

 from this locality and from near the Lower Theoclule hut. Both consist almost 

 wholly of antigorite (without residual augite) : the former might have- come 

 from Sprechenstein, in the latter the mineral is rather smaller. 



2 They are also a little harder than ordinary serpentine. A slaty specimen 

 from a small pit by the path from the Riffelalp Hotel to the Findelen 

 Glacier, contains narrow and thin blades, up to about three-quarters of an inch 

 long, of a pale-green mineral which proves to be actinolite. 



