20 Dr. F. M. Sfripf — Crystalline ScJiids of the Lepontine Alps. 



between Giirtnelleu and Amsteg (pi. ii.), and south of it in the Jorio 

 pass, E. of the railway line ; and the calcareous gneiss near Castione, 

 with imbedded seams of marble (pi. x.), probably belongs here, 

 though it is in a more advanced state of metamorphism. 



0. The Ursern gneiss IV. is broken through by the granitic gneiss 

 belonging to the Finsteraarhorn massif, over which the railway line 

 runs from Goschenen to Gurtnellen (pis. ii. iii.). It differs from 

 the gneiss of the St. Gothard and Ticino valley, not only by its com- 

 pact structui-e, and the peculiar habitus of the quartz and felspars, 

 but also by the predominant iron-magnesian-mica on the side of 

 pellicular potash mica. I have marked it on the summary profile by 

 0", thus indicating that it belongs to a series distinct from I.-IV. 

 It is not eruptive or plutonic in the ordinary sense of the vi'ords, but 

 it belongs rather to an horizon deeper than the lowest (I.) opened 

 in the tunnel, and if thrust up in a solid state, it must consequently 

 have been after the Gothard series, either in immediate connexion 

 vv^ith the general disruption of the mountain or during subsequent 

 paroxysms. Granulitic contact rock limits the granitic gneiss on its 

 northern and southern boundaries (pis. ii.-iii.). 



Eruptive rocks 7- — In connexion with the upthrusted but not 

 eruptive granitic gneiss of the Finsteraarhorn massif, we have finally 

 to consider two rocks of the St. Gothard which seem to be intrusive, 

 viz., the serpentines and the granite. The peridotic serpentines already 

 mentioned as embedded in the micaceous gneiss III. have been de- 

 scribed petrographically in the Geol. Durchs. u. Tabellen, Nordseite, 

 p. 114-123, and in the text to the geol. profile, German, p. 34; 

 French, p. 38. With regard to their mode of occurrence some 

 diagrams are given in " Materialen fiir das Gotthard profil ; Verhandl. 

 der Schweiz. Naturf. Gesellsch., 1878." In spite of the seeming 

 discordance between the serpentine and the surrounding micaceous 

 gneiss, which is very plainly seen in the figures of the treatises 

 quoted above, I believe that the serpentine originally formed lenticular 

 beds in the sedimentary series of crystalline schists, which in the 

 process of general destruction have been severed in pieces and 

 together with the wall-rock thrust along on the fissures. Wherever 

 such a faulted fissure forms the local boundary between serpentine 

 and micaceous gneiss, the former appears to penetrate the latter. 



Granite. — A belt of granite extends eastwards from the Pizzo 

 Eotondo on the north side of the Ticino valley, and disappears, after 

 passing the Val Tremola, without reaching the line of the tunnel 

 (pi. v.). It is a typical granite which does not belong to the St. 

 Gothard series of crystalline schists ; it has a compact granitic struc- 

 ture, and is distinguished by the light rose colour of its quartz. On 

 the Alpe Fieudo (below the Fibbia), in Val Tremola, and near the 

 Sella bridge (below the hospice), direct contacts between this granite 

 and the micaceous gneiss (III.) show its intrusive character (sketch 

 on pi. V. of geol. map. along the railway line), but stepping over the 

 granite from its point of contact south of the Sella bridge, towards 

 the Hospice, one observes a gradual transition into the so-called 

 Gothard granite (Fibbia gneiss), or what I have designated as Sella 



