GO Professor T. G. Bonney [April 4, 



tlie series is inverted in order — the great group of hornblendic 

 and garnetiferous mica schists, which continue along the Val Tremola 

 and the lower slopes of the mountain to the neighbourhood of Airolo, 

 where some calcareous rock occurs, being probably an infold of much 

 later date. 



Through the kindness of Mr. Fletcher and Mr. Davis, of the British 

 Museum, I have been allowed to examine the series of specimens from 

 the St. Gothard tunnel in that collection. They correspond in 

 general with the succession above indicated, except that I have failed 

 to identify the granitoid rock of the summit plateau. Leaving, 

 however, for a moment the question of correlation, we see that the 

 St. Gothard section presents us with an instance of folding on a 

 gigantic scale, and of the fan structure, doubtless with many minor 

 flexures and faults. 



In the neighbourhood of the Val Piora we get an important 

 succession. The ascent to the hotel from the Val Bedretto passes in 

 the main over a series of micaceous schists, and rather friable gneisses, 

 which are a prolongation of an axis exposed in the mountains south 

 of Airolo and fairly correspond with much of the rock (excepting the 

 granitoid) forming the upper part of the St. Gothard Pass. To this 

 succeeds a series which, though more calcareous, clearly represents 

 the garnetiferous actinolitic series of the southern slopes, and to this a 

 group closely resembling the Lustrous Schists. 



I pass now to the section of the Simplon. On the southern side, 

 deep in the glen of the Doveria, in the vicinity of the gorge of Gondo, 

 we find a mass of granitoid gneiss, which recalls to mind that already 

 described from the wildest portion of the upper valley of the Eeuss. 

 We may, I think, with confidence affirm that, whatever be the true nature 

 of this rock, we are again touching the foundation-stones of the rock 

 masses of the Alps. As we approach Algaby, the granitoid gneiss 

 becomes more distinctly bedded and variable, a thin band of 

 micaceous crystalline limestone is passed, and presently the more 

 rapid ascent of the pass begins. Hence to beyond the summit we 

 traverse, so far as can be seen, a great series of bedded gneisses, 

 often coarse and even porphyritic, and of schists. The same are displayed 

 in the crags of Monte Leone on the east and of the Eossbodenhorn on 

 the west. As shown in Professor Renevier's valuable section, bands 

 of crystalline Dolomitic limestone, and of hornblendic and garneti- 

 ferous schists occur in various places on either side of the Simplon 

 road. Then, after descending about half way to Brieg, we strike 

 the group of the Lustrous Schists, with the usual calcareous zone in 

 the lower part. Professor Renevier does not attempt to unravel the 

 complexities of the strata which compose this portion of the central 

 ridge of the Alps, and I feel that my slighter knowledge makes caution 

 y et more imperative ; but I think we are justified in asserting that we 

 have evidence of an upward succession from the coarse granitoid 

 fundamental gneisses, through more variable and bedded gneisses, to 

 a group which recalls the garnetiferous schists, so finely developed on 



