RELATION TO MESOZOIC ROCKS IN THE LEPONTINE ALPS. 207 



schist (as before) ; (2) Disthene schist ; (3) Gneiss rather crushed ; 

 (4)]^llauchwacke. 



Fig. 3. — Section in upper part of Ravine^ south-east of 

 Lalce llitom. 



A. Dark-mica schist. E. Disthene schist. G. Gneiss. R. Eauchwacke. 

 The part left blank is covered ground. 



In these sections (A) is a thick mass, well exposed in a line of 

 crags ; (B) in the latter is a thin band, the absence of which from 

 the former section is of little importance, for it may be concealed by 

 debris or have died out : but after this we find in the one case calc- 

 mica schist in its ordinary position, and apparently overlying the 

 rauchwacke, while in the other it is wanting, and its place is taken 

 by a rather thin mass of gneiss (which ought to underlie the rauch- 

 wacke). If, then, we adopt the idea of a regular sequence and 

 simple fold, we are involved in hopeless confusion ; while an exami- 

 nation of the rocks in the field itself suggests that the rauchwacke 

 is caught between two sets of thrust-faults, one of these being, very 

 probably, the southern main fault already mentioned. 



AVe pass on to the section already incidentally mentioned near 

 and about the summit of Pongio (fig. 4). Here we find, apparently 

 in descending order : — (1) Dark-mica schist; (2) Rauchwacke ; (3) 

 ])ark-mica schist, with Black-garnet schist ; (4) Calc-mica schist ; 

 (5) Gneiss (crushed). Here, then, the rauchwacke appears to be 

 intercalated in the Dark-mica schist. These sections also, if read 

 from the south side, would indicate that the Calc-mica schist was 

 the lower rock, while if we read from the north side it would be 

 the Dark-mica schist. Obviously, then, the idea of a simple trough 

 is inadmissible. Furthermore, this strip of rauchwacke, where it 

 is exposed in the ravine leading down from the alp between Fongio 

 and the Plan Alto, contains numerous fragments of schists which, to 

 our eyes, were undistinguishable from members of the calc-mica 

 schist group, which crop out in the same ravine, as already stated. 



