2-30 TROF. T. G. BOXXEl ON CKYSTALLIXE SCHISTS AND THEIR 



(b) The llauchwaclce, 



So far as concerDS the mineral constituents, I have nothing to 

 add to Dr. Grubenraann's petrographical studies. Indeed, I have 

 had only a few slides ])repared, because the question which I sought 

 to determine was petrological, viz. whether the composition and 

 structure of the rock permitted of its being placed at the base of a 

 certain group of crystalline schists, a question which, to my mind, was 

 decisively answered. Dr. Grubenmann describes the lower zone of 

 rauchwacke in the Yal Canaria section more minutely than the 

 upper, but gives analyses of the latter *. I have onl}'- looked at 

 this through the microscope, and have thought it needless to examine 

 the anhydrite or gypsum, or one of the more dolomitic bands. But 

 that the two zones belong to the same mass of rock there can be 

 no doubt. Quartz, pyrite, mica, talc, tourmaline, disthene, rutile, 

 and zircon are the chief minerals enumerated' by Dr. Grubenmann 

 and by earlier observers as accidental constituents of this series. In 

 a specimen from the upper zone he obtained an insoluble residue of 

 about 2 per cent., consisting of colourless flakes of a biaxial mica, 

 with a small axial angle (margarite), and greenish flakes of a uni- 

 axial mica (biotite), quartz-grains, and little cr5^stals of tourmaline, 

 rutile, and zircon. 1 selected for examination two specimens: one, 

 a clear, fairly hard, cream-coloured rock, in which onl}^ a few tiny 

 flakes of white mica and specks of some dark mineral could be seen 



According to Dr. von Fritsch {J. c. p. 113), Esclier von der Linth found in 

 the calc-mica schists of the Lepontine Alps '' unhestlrjimfe aher unzwelfelhaft 

 organische rested Of these I have never seen the slightest indication, and 

 venture to think this evidence insuflicient. Studer also states that he found 

 belemnites in tlie Knoten-i^ckiefer, at Fontana, in the Val Bedretto. T did not 

 myself come across either this rock or the black-garnet schist at that locality, 

 but it is not mapped there by Von Fritsch, and so, being anxious to spend my 

 time on the important Nufenen mass, I made no search for it. Mr. W. Watts, 

 however, informs me that he failed to find it, though he spent some time 

 hunting about. I would venture to suggest that the mass examined by Studer 

 was not in situ. The number of the erratics in the upper part of the Val 

 Eedretto is enormous. 



* Analysis of a saccliaroidal white dolomite, from a quarry north of Villa 

 (Val Bedretto) : 



I. II. 



CO., 4601 45-97 



OaO 39-04 .39-14 Sp. gr. =2-8469. 



MgO 1.504 1516 



100-09 100- 



Also of a fine-grained, rather yellow-coloured dolomite from the ravine (Val 

 Canaria) : 



CO., 44-9() 45-15 



CaO 40-12 4016 



MgO 11-96 11-98 Sp. gr. =2-8303. 



FeO 42 0-36 



Insoluble residue 1-96 2-05 



99-42 99-70 



