A Pebbly Quartz-schist, Pennine Alps. 403 



appears to warrant the identification of the Pontiskalk with the 

 calc-mica-schist. But even a brief examination of the slopes on 

 which the former rock occurs shows us that we are dealing with 

 a very complicated piece of geology, and I have little doubt' that 

 the Pontiskalk is a much newer rock than the calc-mica-schist and 

 its associates. But to give my reasons for this opinion — and these 

 are not of an a priori character — would extend this paper to an 

 unreasonable length. 



The quartz-schist certainly varies considerably in thickness. But 

 I made no measurements, for in a district like the Alps their value 

 must often be uncertain, and this point had no bearing on the 

 questions with which I was concerned. In places I think it exceeds 

 a hundred feet. It also varies in character. It is distinctly pebbly 

 near Fang, to the ESE. of the Weisshorn Hotel (i.e. under the 

 Tounot), and on the left bank of the valley opposite to Zinal 

 (though here the pebbles are generally small). It is often rather 

 coarse and slightly "gneissose" in texture, owing to the presence 

 of a filmy, pale-green mineral, but from this condition it passes 

 into a nearly homogeneous, white rock, — as in places opposite to 

 Zinal, and at the Alpe de Collier (on the right bank, about 1500 

 feet above the village). As a rule, the quartz-schist is not only 

 less slabby than it is above Saas Fee (though that structure may 

 be observed near the alp just named), but also (so far as I have 

 seen) it wants that occasional distinct banding with a grey mica. 

 The most pebbly part — where we examined it in situ south of Fang 

 — was some four feet thick. The pebbles were in layers, the 

 thickest of these being about fifteen inches, but they were not 

 restricted either to the bands or to this part of the rock. They 

 generally varied from well-rounded to subangular, and often seemed 

 slightly distorted by pressure. Most of them were white vein- 

 quartz, but I also noticed a reddish quartz (small), and a compact 

 light-gi'een rock, rather soft and flatter in shape, which sometimes 

 seemed to merge into the films already mentioned. 



In addition to the specimen from near the Weisshorn Hotel, 

 I have examined microscopic sections from the following localities : 

 Fallen pebbly blocks north of Fang; pebbly band in situ 

 south of Fang; slabby, slightly fissile quartz-schist near Alpe 

 de Collier ; rather pebbly rock opposite to Zinal ; most compact 

 and white variety, in same mass. I may refer to my former 

 paper for a general account of the microscopic structure of the 

 quartz-schist, and content myself with calling attention to any 

 differences exhibited by these specimens. In most of them the 

 constituents vary much more in size than in those from Saas Fee, 

 but the " matrix " in which the larger fragments are set is more 

 fine-grained. The most uniform in character, as might be expected, 

 are the examples from the Alpe de Collier and from opposite 

 to Zinal (compact variety). The former consists usually of quartz 

 granules rather less than -0025" in diameter, and of mica flakelets, 

 which seldom attain -025" in length. But even here the matrix 

 becomes a little coarser in places, the quartz-grains occasionally 



