Dr. Irving — On the Airolo Schists. 257 



2. The first (lowest) zone of 2-mica Schists : grey-green to dark- 

 green, becoming in places talcose and chloritic, very lustrous, con- 

 taining, here and there, in addition to the two micas, lamella? of 

 disthene, also quartz-veins accompanied with calcite and kyanite : 

 the single bands of schist not generally exceeding 5 cm. (2 in.) in 

 thickness. Tourmalines, rutiles, zircons, zoisite, and magnetite are 

 met with in these schists. (2 metres.) 



1. The lower zone of gypsum, rauchwacke, and dolomite : in the 

 gypsum occur quartz, pyrite, mica, talc, tourmaline, disthene, and a 

 few zircons ; in the dolomite, fragments of glassy quartz and calcite. 



So far as the detailed descriptive work of Dr. Grubenmann goes, 

 it is simply admirable ; it is in the interpretation of the facts, as 

 pointing in the direction of a general theory of ' dynamo-meta- 

 morphism,' that we feel compelled to part company with the author, 

 and that for the following reasons : — 



(1.) The assumption l that these rocks all belong to one and the 

 same complex (Schichtenreihe) seems to be quite arbitrary, since in 

 such a highly disturbed and deformed district as this 2 their present 

 juxtaposition may be (and probably is) merely accidental. 



(2.) Although the garnet-bearing schists of the Val Canaria have 

 been well worked out, the author, in identifying them with the 

 altered rocks (containing Belemnites) on the Nufenen and Gries 

 Pass to the west, and of Fontana to the east, has fallen into a 

 fatal error, from not testing the spurious knotty structures in the 

 limestones, which in the pre-microscopic days of petrology were 

 described as garnets. On Prof. Bonney's closer scrutiny of them 

 this identification breaks hopelessly down. These knotty structures 

 are found to belong to a very low order indeed of silicates, and are 

 admittedly not garnets at all. There remains, therefore, no evidence 

 that these garnetiferous ' schists ' are of Jurassic age. 3 



(3.) If it be admitted that the dolomites, rauchwacke and gypsum 

 are of Tnassic age, this tells us nothing about the age of the schists 

 with which they are in accidental juxtaposition; since by Dr. 

 Grubenmann's own showing the insoluble residues of the gypsum 

 contain minerals furnished by the weathering of the schists. What- 

 ever therefore the age of the schists, they must be certainly much 

 older than the gypsum. But the examination of the district by 

 Dr. Bonney and Mr. Eccles has brought to light even more cogent 

 evidence than this; for they find that the dolomite is frequently 

 brecciated, and that the included fragments are derived from these 

 very schists (with their characters well preserved), which are 

 supposed to be younger than they. It is somewhat strange that 

 such evidence has been overlooked, or ignored by Di\ Grubenmann 

 in compiling his memoir. 



(4.) In the assumption that certain markings in the calc-mica- 

 schists in Val Piora, observed by Escher v. d. Linth many years ago, 



1 Ibid. p. 3. 



2 See published sections of the Gotthard Tunnel by Dr. Stapff; Prestwich, 

 Geology, vol. i. p. 304, section i. 



3 See Grubenmann, Ibid. p. 17. 



DECADE III. VOL. VII. — NO. VI. 17 



