290 PROF. T. G. BONNET ON MESOZOIC ROCKS AND [Aug. 1 894, 



second outcrop of marble, much smaller than the other one, forming 

 a low craggy rib, which, however, can be followed for some distance 

 up the hillside before it finally disappears. Lastly, after crossing 

 another slope of turf, about 50 yards in width, we come to the 

 gneiss already mentioned. Thus the upper section exhibits (as was 

 the case in the St. Gothard tunnel) two masses of marble. Of these 

 the one common to both sections is at a considerably greater 

 distance from the gneiss in the upper than in the lower section. 

 This obviously is suggestive of faulting. 



Microscopic examination of the more micaceous and more quartzose 

 rocks mentioned as occurring on the northern side of the marble 

 shows them to possess the ordinary structure of a crystalline schist 

 which has been subsequently somewhat modified by pressure. They 

 consist of quartz, possibly some felspar, and mica (chiefly white) ; the 

 former rock contains a few grains, rather rectangular in outline, of 

 some rather decomposed aluminous silicate, and the mica is in some- 

 what larger plates and occurs in more definite films ; the latter rock 

 includes one or two zircons. Both are somewhat stained by a 

 brownish or blackish substance (probably a hydrocarbon) which 

 appears to be an infiltration. It must be remembered that the 

 marble itself becomes not only micaceous, but also quartzose, the 

 latter mineral sometimes dominating over the calcite, and the rock 

 precisely resembling one of the more quartzose calc-mica-schists so 

 common in the Alps. In other words, we have to deal, in this 

 particular section, not with a single rock, but with a group of 

 crystalline schists, in which a calc-schist or marble dominates, each 

 presenting the aspect and structure which are elsewhere characteristic 

 of crystalline schists (somewhat affected by pressure), and which 

 I have never seen in the Mesozoic rocks of the Alps or of any other 

 country. 



Lastly, it must not be forgotten that on the southern side of the 

 ' sericite-gneiss,' between it and the Hospenthal schists, is a belt of 

 sedimentary rock consisting of a dark phyllite, with some bands of 

 coarser material, which, on the Swiss Geological Survey map, is 

 referred to the Carboniferous System. The ' sericite-gneiss ' is 

 most probably a modified granite, but whatever be its age (and this 

 can hardly be post-Jurassic), a study of these sections alone is 

 enough to show that the collocation of the various masses between 

 the micaceous gneiss on the north and the Hospenthal schists on 

 the south cannot be explained by a simple folding. 



The St. Gothard tunnel, according to the map in Baedeker's Guide, 

 passes beneath the meadows slightly to the west of the lower of these 

 two sections at Altkirche. Since my return I have again examined 

 the series of specimens from that tunnel which are preserved in the 

 British Museum. 1 They exhibit the following succession, going 

 southwards: — (1) Gneiss; (2) phyllite; (3) marble or calc-schist; 



1 I have to express my sincere thanks for the facilities afforded rne by Mr. L. 

 Fletcher, the Keeper of the Department of Mineralogy, and for the help of 

 Mr. G. H. Prior, F.G-.S. 



