Yol. 50.] CRYSTALLINE SCHISTS IN THE LEPONTINE ALPS. 297 



parts of the Alps, or to find a cause for the metamorphism, or to 

 account for its capricious action. Instead of keeping to the realm of 

 law we are driven into the realm of miracle. The other hypothesis, 

 which affirms the Altkirche marble with its quartzose associates to 

 be a portion of an old floor of crystalline rocks on which the Jurassic 

 rocks were deposited, and of which in process of faulting wedge-like 

 masses were subsequently thrust through the overlying later deposits, 

 can be supported on the grounds indicated above, but is open to the 

 objections that the general coincidence in strike between the marble 

 and the Jurassic rocks is singular, and the depth to which this 

 simulated interbedding of two masses of very different age extends, 

 as proved by the tunnel-sections, is unusually great. Still, if any 

 trust may be put in comparative petrology, as it may be called, the 

 difficulties in the latter hypothesis are much the less serious. 



III. The Val Canaria Section. 



Though it appeared to me that Prof. Heim's objections to my 

 interpretation of the section of the ravine in the Val Canaria had 

 but little weight, I thought it well to take an opportunity of revising 

 our work. Of its general accuracy I felt confident: still, as we had 

 not been a second time over the ground, mistakes or omissions in 

 points of detail were very possible. Indeed, I suspected a clerical 

 error in an aneroid observation, for the thicknesses assigned to the 

 upper rauchwacke and the schist did not agree with my general 

 recollection, 1 while that of the lower rauchwacke was only an 

 estimate. The following results are, I believe, fairly correct. The 

 vertical height of the outcrop of the upper rauchwacke is about 520 

 feet, of the schist 250 feet, of the lower rauchwacke 400 feet. I 

 can add little to the account of the schists already given, for unfor- 

 tunately they were not nearly so well exposed as they had been in 

 1889. A huge mass had fallen from the crags of rauchwacke 

 (upper) on the right bank of the ravine, and its bed was completely 

 buried by debris for a considerable distance below. Still, I was able 

 to investigate one or two details of some little importance, especially 

 as to the relations of the rauchwacke and the schists. The junction 

 of the upper mass of the former rock with the top of the latter is 

 not easily determined with precision, for the rauchwacke at this 

 part contains flakes of mica abundantly, is much smashed about, 

 and is very fissile. The schist, seemingly a variety of the disthene- 

 schists, 2 is twisted, quartz-veined, apparently includes little lenticles 

 of the rauchwacke, and presents an aspect very suggestive of 

 ' mylonitic ' action, that is to say of the existence of thrust-planes. 

 The junction of the schist with the lower mass of rauchwacke is not 



1 It was, however, the latter rather than the former which was in fault. 



2 I retain the name for reasons given in the last paper ; but it must be 

 remembered that disthene (or kyanite) is commonly only a microscopic con- 

 stituent, and the rock is a rather soft and friable schist, chiefly consisting 

 of two species of mica (see Quart. Journ. Greol. Soc. vol. xlvi. p. 227, for 

 description). 



