220 PROF. T. G. JiONNEY ON CRYSTALLINE SCHISTS AND THEIR 



schists, and at some little distance to the south a great mass of the 

 Calc-mica schist. This accords with what I saw in crossing the 

 (jries Pass *. This differs from the Nufenen Pass in runnina: 



completely across the different rocks mentioned in the above 

 description ; for at the Tosa Ealls we are again on gneiss. The 

 summit of the Gries Pass is about a mile and a half, as the crow 

 flies, from the " col " of the Nufenen. On the last part of the ascent 

 to it, from the north side, we traverse "■ spotted rock " close to the 

 top, and at the commencement of the descent is Black-garnet schist, 

 followed by other schists of the Piora group f. 



From the description given above it is obvious that even in the 

 field the resemblance between the " spotted rock " and the Black- 

 garnet schist, as a rule, is rather superficial. But on a closer study 

 of the former the differences become yet more marked, as will be seen 

 by comparing the following description with that given above of the 

 schist. The description is chiefly founded on specimens from the 

 Nufenen, which, as it appeared to me, are better imitations of 

 crystalline schists than those from the Lukmanier, but mutatis 

 mutandis it will apply generally. The " spotted rock," even in the 

 most crystalline specimens that I could find, presents marked 

 differences from the Black-garnet schist. Por instance, on examin- 

 ing the fresh cross fracture of a slab we find it exhibits a much less 

 definite foliation ; sometimes, indeed, its structure hardly differs from 

 that of an ordinary dark argillaceous limestone which has lindergone 

 considerable pressure, showing a rude cleavage with a dull 

 glimmering surface. On these fresh fractures the eye less readily 

 detects the included minerals, and instead of the fairly well-defined 

 faces or the resinous lustre cf the black garnet, we only detect not 

 very clearly defined and but rarely lustrous spots. Instead of the 

 rather bright " sheen-surfaces " of the schist, we find a dull glim- 

 mering surface, like imperfecth' polished " black lead,"' which, on 

 applying a lens, is seen to be a dead blackish mass powdered with 

 glitt.ering specks. When we study the included minerals (for 

 Avhich purpose we must select a well-weathered surface), we find 

 that instead of garnets, presenting their usual crystalline form 

 (though it be occasionally somewhat distorted or flattened), we have 

 rounded bodies, seldom exceeding about a quarter of an inch in 

 diameter, which in form are commonly rather flat oblate spheroids, 

 and sometimes rudely ellipsoidal. The surface of a garnet projecting 

 from the schist, except where corroded by the weathering-out of the 

 included impurities, is fairly lustrous ; the spheroidal bodies are dull 

 and minutely granular in aspect. In the case of the associated 

 prisms the external angles are generally ill defined, and they too are 



* I examined it in 1883. 



I" My knowledge of this pass was one of the chief grounds of my scepticism 

 as to the occurrence of " fossils in crystalline scliists." Fortunately I had 

 written careful notes (though then much perplexed by this "spotted" rock) and 

 had brought away specimens. I think it probable that the whole of the " bulge " 

 to the north shown on the Swiss Survey Map is the outline of the Kalhhaitig 

 GU'iniiicr-schiefer, roughly cut off by a line drawn from the Val Corno to the 

 Mittaghorn, and will be foiuid to consist of Jurassic rock. 



