RELATION TO MESOZOIC EOCKS IN THE LEPONTINE ALPS. 209 



Grubenmann and others we have here the two ends of a fold of 

 rauchwacke enclosing the overlying schists, the axial plane of the 

 trough dipping (as is so commonly the case) to the north. But 

 when we come to study the annexed section (fig. 5) minutely we 

 find that, though at first sight the Calc-mica schist seems to rest 

 upon the rauchwacke and to be succeeded by the Elack-garnet schist, 

 we cannot make out any definite order in the upper portion of the 

 fold (where, of course, the lower should be repeated). Again, as we 

 pass over the outcropping beds in the ravine, we notice constant 

 evidence of squeezing, sometimes of crushing, with gliding planes 

 and other indications of thrust-faulting. But when we have passed 

 through the upper mass of rauchwacke, we are confronted by a 

 further difficulty : we find ourselves, after crossing a very few feet 

 of a mica-schist or gneiss, separated from the mass of the Tremola 

 schists by a comparatively thin zone of black-garnet schist and 

 silvery mica- (? disthene) schist *, which are undistinguishable from 

 those included in the fold below. 



The identity of the latter, as a group, with the Piora schists cannot 

 for a moment be doubted. If, then, the hypothesis that in some 

 way or other we have the thick mass of the Piora schists compressed 

 into a fold measuring only a few hundred feet across, be correct, 

 what explanation is to be given of the occurrence of certain of its 

 components below the rauchwacke, which is the basal member of 

 the trough ? 



But this is not all. Let us now examine the rauchwacke on 

 either side of the supposed fold. In the lower member mica, mostly 

 silvery, is fairly common. This, in its form and distribution, sug- 

 gests a detrital origin, and there are sundry small flaky bits which 

 are curiously like fragments of schist. Similar mica occurs in the 

 upper member, but here, near the top, we find that the rock becomes 

 a true breccia full of angular fragments, sometimes more than two 

 square inches in area, similar to schists which occur in the ravine 

 below t- That these fragments were broken from members of the 

 Piora series we had not the slightest doubt. It is therefore evident 

 that in this Yal Canaria section we are dealing not with a simple 

 trough, but with an overfold broken up by a series of thrust-faults, 

 as shown diagrammatically in the annexed figure (fig. 6), — that the 

 apparent infolding of the Piora schists by the rauchwacke is wholly 



* Dr. von Fritsch maps these two beds as identical with the disthene-schist 

 and garnet-schist below and in the Val Piora. Dr. Grrubenmann, though he 

 says he did not see any disthene nnder the microscope, admits the identity of 

 tlie former with the "two-mica"' (disthene) schist below. To myself they arc 

 macroscopically nndistinguishable. I was not fortunate enough to find a very 

 characteristic exposure of the black-garnet schist, but scattered blocks are nume- 

 rous, and I have no doubt of the accuracy of Dr. von Fritscli's mapping. I 

 find, on examination, that the "disthene" schist contains grains of a mineral 

 like staurolite, and I think I can detect disthene (see p. 227). 



t We did not, indeed, discover the black-garnet schist, but found the so-called 

 disthene schist and other silvery and greenish micaceous schists which occur in 

 the Piora series; these fragments, however, appear to be less modified by subse- 

 quent pressure than the rocks in sif/c below. 



