RELATION TO MESOZOIC liOCKS IN THE LEPONTINE ALPS. 213 



therefore save future trouble to say that the possibility of such an 

 error was always present to our minds, and that we convinced 

 ourselves, at any rate when the rock was i7i situ, that we were not 

 making any mistake. On this point we were especially careful in 

 the Yal Canaria section, which alone would be sufficient for our case. 

 But since my return to England I have obtained evidence which 

 seems to me to place the accuracy of our observations beyond 

 question. The upper band of rauchwacke in this section — that in 

 which we found the fragments of schist — is continuous with the 

 mass which at a little more than a mile distance along the outcrop 

 is pierced by the St. Gothard tunnel at Airolo. In the British 

 Museum is a collection of rocks illustrating the masses traversed by 

 this great work, which by the courtesy of the authorities of the Mineral 

 Department, I have examined. At the south end of the tunnel a 

 considerable thickness of rauchwacke was pierced, and the collection 

 contains several specimens of the rock. In at least three, taken 

 from between 60 to 72 metres from the entrance, fragments of 

 schist, like those in the Yal Canaria, distinctly occur. Another, 

 found at 78*5 metres, has similar fragments of considerable size. 

 Another, at 83 metres, exhibits two parallel slabs of the " two-mica " 

 (so-called disthene) schist, which I have described above, cemented 

 by rauchwacke. This has been taken either from a mass of coarse 

 breccia or from a very unequal junction-surface of the schist and 

 rauchwacke. At 85 metres is the schist itself in situ. Thus this 

 section and that in the Canaria ravine are as nearly as possible 

 identical, and it is impossible to deny that the breccia occurs at the 

 base of the rauchwacke. 



4. The Jurassic Eocks containing Possils and Minerals. 

 (a) Preliminary. 



The occurrence of fossils in the dark, slaty, sometimes schistose, 

 but non-crystalline rocks of tlie Alps has long been well known. 

 Most of these instances have no more bearing on questions of 

 metamorphism than the occurrence of fossils in certain districts of 

 Devonshire or North Wales. The rocks arc slates, at most phyllites, 

 not true schists, and probably no rcfereuce would ever have been 

 made to them in the literature of such questions, had not so much 

 confusion been produced by the vague use of the term schist. 

 Studer, however, many years since spoke of finding Jurassic fossils 

 in the same rock as garnets, and, as I have already said, specimens 

 illustrative of tliis were exhil)ited by Dr. Heim at the meeting of the 

 Geological Congress in 1888, which, through his courtesy, I M^as 

 enabled to examine, so far as could be done with a lens. They 

 were of much interest, and in one or two cases certainly bore a 

 strong resemblance to the Black-garnet schist described above. 

 Still I was not quite satisfied of the identity of the rocks, and some 

 scepticism seemed more than justifiable, for it was very difficidt to 

 understand how such a fossil as a Belemnite could have retained 



