216 PROF. T. G. 3iON:NEi' 0^ CllYSTALLI^NE SCHISTS AND THEIK 



It is a dark- coloured, somewhat schistose rock, having a mde 

 cleavage variably developed, and occasionally is quite an ordinary 

 '• bastard slate." The ground-mass has commonly a n on- crystalline 

 aspect, though the rock contains much mica, which appears on a 

 weathered surface like tiny spangles, and frequently the minerals 

 ;)lready mentioned are abundant. These at first occur rather 

 sparsely, but soon become more numerous. After crossing a second 

 ravine, at a height of some 800 feet above the pass, fossils are found 

 in the " spotted rock." 3elemnites, though not in very good condi- 

 tion, are readily recognized, and a little further on the joints of 

 Pentacrinites can be identified. With both are found the round 

 minerals — about as big as hemp-seeds — and the prisms up to full 

 one third of an inch long. Fossils then for a time become rare or 

 are absent, but the " spotted rock " continues, occasionally inter- 

 banded with a hard sandstone or impure quartzite. Sometimes, 

 however, the "spots" disappear, and the rock becomes quite an 

 ordinary black " satiny " slate. We next cross a rather flaggy, 

 fine-grained sandstone, which forms a crag more than 20 feet high ; 

 then comes another mass of " spotted rock " followed by sandstone 

 bauded with slate ("spots" rare); then a dark, rough, slaty 

 " spotted rock " followed by sandstone ; to this succeeds a great 

 mass of an extremely fissile rock of variable mineral character. 

 Evidently it has been intensely crushed, and is thus in a very- 

 unfavourable condition for examination ; but this may be affirmed 

 with confidence, that it is a member of the crystalline series. The 

 upper part exhibits roundish spots like fragments of decomposing 

 felspars, so that it may once have been a gneiss, or even a fine- 

 grained rather micaceous granite. Parts, however, of the mass 

 have possessed a stratification-foliation ; for this occasionally can be 

 seen to " wriggle " across the newer structural planes of the 

 " cleavage foliation," which cut the former like a " strain-slip " 

 cleavage. 



To this mass, which I have no doubt is an upthrust portion of the 

 old crystalline floor, succeeds another mass of " spotted rock " (the 

 " spots " perhaps attaining a rather larger size than before) with 

 sandstone bands, much twisted, crushed, and altogether in great 

 confusion. This is succeeded by another mass of shivered schists, 

 and that, again, by more " spotted rock," which appears to continue 

 along the southern face of the mountain *. We had thus examined 

 a large tract of the " spotted rocks," and to my eye, in the field, even 

 the specimens richest in minerals were readily distinguishable from 

 an average specimen of the Black-garnet schist of the Val Piora. 



* Yon Fritsch marks on his map a band of rauchwacke running up the flank 

 of Scopi, apparently about in the position of the line of sandstone crags 

 mentioned above. We, however, did not find any rock that we could identify 

 with the rauchwacke group, except that a small crag at the base of the slopes 

 overhanging the main stream consists of a pale fawn-coloured rock, wliieh, 

 though rather harder than usual, may be one of the dolomites in this group. If 

 so, it would be an outlier of the great mass of rauchwacke which, as already 

 mentioned, occurs near the top of the pass. We find that in this respect we are 

 in accord with the more recent map published by the Swiss Geological Survey. 



