EELITION TO MESOZOIC EOCKS Ilf THE LEPONTINE ALPS. 193 



On the present occasion we chiefly devoted ourselves to the exami- 

 nation of the rocks lying between the " Urseren gneiss " and the 

 " sericite gneiss." They are not very well displayed, for so much 

 of the hillside is covered by turf. Briefly related, this is what we 

 found. Beginning on the northern side, and keeping near the base 

 of the slope, we passed over a crushed-looking gneiss. This, which 

 (to quote from my note-book) " was examined again and again dur- 

 ing the day, may be the ' Devil's-bridge ' gneiss in a very crushed 

 condition, still it has a more friable, saccharoidal aspect, and thus 

 bears some resemblance to the gneiss of the St. Gothard Pass." 

 After a brief interval of turf, we came to a very fissile, black, slaty 

 or schistose rock, shortly followed by calc-mica schist *, which indu- 

 bitably graduates into the marble quarried at the back of the chapel. 

 This rock on its southern side passes back again into a calc-mica 

 schist. Yet further to the south we came to the " sericite gneiss." 

 Two other traverses made higher up the slope gave us the same suc- 

 cession, though certain changes presently to be described take place 

 in the marble, which does not long retain the whiteness and com- 

 parative purity exhibited in the quarry. We failed to discover 

 any fossils at the locality indicated on the map ; and we could 

 only find a very small patch of a friable cream-coloured limestone 

 in the bed of a glen to represent the rauchwacke. At a rather 

 higher level, however, we came uponasmall outcrop of dark unaltered 

 rock which bore a considerable resemblance to the ordinary Jurassic 

 rock of the district. It is therefore possible that a small outcrop of 

 this age containing fossils may occur on the right bank of the Eeuss 

 valley ; but we failed to find it, though we searched carefully, and 

 visited, as we believe, every outcrop between the '• Urseren " and 

 the " sericite " gneisses. 



This section then exhibits rocks, which appear not highly altered 

 close to a distinctly crystalline calc-mica group. Let us now subject 

 them to a more minute investigation, taking first the crystalline 

 group. The marble has a flaggy structure. The surface of the slabs 

 exhibits frequently filmy flakes of white mica, and not seldom the 

 superficial " flutings " which indicate earth-movements. In one part 

 of the quarry the marble is banded with layers of mica, often about 

 1 inch thick, and it passes, as has been said, into a calc-mica schist. 

 On microscopic examination we see that the rock gives some indications 

 of pressure, but that in many parts it exactly resembles one of the 

 ordinary white marbles which, in many other districts of the Alps, 

 are associated with true crystalline schists. It is never quite free 

 from flakes of white mica, and grains of quartz, obviously authigenous, 

 are not rare. There is nothing to suggest that the crystalline 

 structure of the rock is in any way the result of pressure ; but we 

 may confidently affirm that such modifications as can be attributed 

 to this agent of change were produced after the rock had assumed a 

 crystalline condition, and when it differed in no material respect 



* In the field the calc-mica schist might be thought to exhibit a tendency to 

 graduate into this phyllite. Tliis, however, proves on further examination to 

 be illusory. 



