Vol. 54.] SCHISTS OF THE ST« GOTHAKD PASS, 361 



blocks. Some of these exhibited distinct alternations of felspathic 

 and hornblendic rock. In one case a sort of tongue of actinolitic 

 diorite, without definite ordering, passed rapidly into a very close- 

 banded or foliated rock more of the Lizard type, but with signs of 

 crushing and a rather actinolitic habit. The evidence, however, 

 as we interpreted it, was favourable to the idea that, while pressure 

 had produced its usual effects, some structures indicated fluxional 

 movements in an ill-mixed or differentiated rock. 



The second section (described in the same order) afforded (1) loose 

 blocks, fallen from the cliffs above. These consisted of (a) gneiss, 

 moderately coarse, rather felspathic, and fairly micaceous, repre- 

 senting a type common in the mountains on this side of the Val 

 Bedretto ; (6) dioritic rock ; and (c) the garnet-actinolite schist, the 



Fig. 1. — Hornblendic streaks in a rather felspathic diorite^ fringed 

 with bristling actinolite-crystals, or passing into a tangle of the 

 latter. {Above Lago Tom.) 





■'^m^l^g^^^^^' 



latter mineral often occurring in bunches, its crystals being frequently 

 some 3 inches long and about as thick as a small bodkin. These 

 were best developed along the planes of cleavage-foliation, and 

 exactly resembled some of the specimens from the southern side of 

 the St. Gothard and the entrance of the Val Can aria. (2) A dioritic 

 rock of the ordinary character, with darker more hornblendic bands. 

 (3) The same, but with the hornblende more distinctly actinolitic. 

 This rock, which exhibits minor variations, extends for a considerable 

 distance. (4) Rather felspathic hornblende-schist, often distinctly 

 banded. In one case the more felspathic and more hornblendic 

 bands (each of which exhibits a faint streaking or foliation in 

 itself) run about 3 inches thick. This rock passed in one place 

 into a biotite-gneiss, with but little quartz ; in another a dark horn- 

 blendic rock ap))ears in a way suggestive of an intrusion. 



What we saw in other places was in general accord with these 

 two sections, and with those on the southern side of the St. Gothard, 

 so that the field-evidence seemed to point to the following con- 

 clusions : — 



(1) More or less gneissoid schists, varying from micaceous to 

 hornblendic, often actinolitic, and sometimes rather rich in 

 garnets, are interbanded : the passage from the one to the 

 other being occasionally rather rapid (in a few instances even 

 suggestive of intrusion), but generally a more or less gradual 

 one. 



