404 T. G. Bonney — A Pebbly Quartz- schist, Pennine Alps. 



ranging up to -02 " ; while the second specimen is throughout 

 rather coarser, the quartz-grains in it attaining ahout double the 

 last-mentioned size. All the other slices exhibit great variety in 

 structure, the matrix being sometimes quite as fine as in the first 

 instance, but generally more micaceous. The included fragments 

 are mostly quartz, and their exterior (and this is also true of the 

 granules) is " ragged " in outline, except in certain cases, when 

 it is surrounded by a kind of envelope of mica, like a pellet wrapped 

 in paper. Of these fragments the smaller are generally simple, 

 the larger composite, being apparently vein-quartz, though one or 

 two of them resemble a rather minute and highly altered quartzite. 

 The others often exhibit strain shadows, are sometimes cracked 

 (occasionally with slight displacement), and are again cemented 

 with chalcedonic quartz. But there are cases where this material seems 

 as if it had been the result of molecular change, without fracture, 

 along a certain direction in the grain ; and when it occurs at the 

 exterior, as it not seldom does, it appears to have been formed 

 by the same process rather than by accretion. Felspar is always 

 present, though generally rather altered ; cleavage may be observed, 

 but I have not come across polysynthetic twinning. No doubt 

 it represents original fragments, though at the present time it is 

 not obviously clastic. Some of the felspar-grains may be seen 

 to pass into a mass of minute mica, cemented by exceedingly fine 

 chalcedonic quartz, and I think that the micaceous part of the matrix 

 has been formed generally by the alteration of clayey or silty 

 matter. The mica exhibits a very faint tinge of a greenish colour, 

 and is probably not materially different from that in the Saas 

 Fee rock. It occurs in fairly regular fiakelets, and in most cases 

 is clearly authigenous, though a few larger flakes possibly may 

 be derivative ; that is probably true of two or three bits of rather 

 altered biotite. As in the other rock, I note occasionally small 

 zircons, rutiles, and epidote or zoisite, with iron oxides and some 

 brownish granules, which I think are garnets, though one or two 

 suggest the possibility of idocrase ; but quartz and mica (almost 

 colourless), with some felspar, are the dominant constituents. One 

 fragment may represent a very fine-grained micaceous schist. This, 

 I suspect, belongs to the compact greenish rock mentioned above, 

 of which, however, I failed to obtain a good piece in a position 

 favourable for a section. 



These specimens from the Val d'Anniviers present more resem- 

 blance to the crushed Torridon Sandstone and the " piped " quartzite 

 mentioned in my last paper, than do those from Saas Fee, but they 

 are by no means identical with either. They have been affected by 

 pressure, but the mineral change is much more complete than in 

 Scotch rocks, and there is nothing to show that this pressure was the 

 chief agent in producing the metamorphism. They retain, probably 

 owing to their greater coarseness and more heterogeneous character, 

 much more distinct traces of their original condition than the 

 quartz-schists from Saas Fee, but their differences from frag- 

 mental rocks in the Mesozoic or later Palaeozoic systems in the 



