of the Lepontine Alps. 11 



German text to profile, p. 22 ; French, p. 24) and thus comparable 

 with the described calc-mica schists of the south side. Macroscopic 

 garnets, distheue, etc., are lacking on the north side, where anhydrite,^ 

 gypsum, and gunpowder-like magnetic iron are interesting accessory 

 constituents of the calcareous sericite schists ; and the presence of 

 rolled grains of quartz prove them to be originally psammitic rocks. 



It should, moreover, be kept in mind that sporadic intercalations 

 of calcspar are by no means rare in the crystalline schists of the 

 St. Gothard. They frequently occur in the green felspathic and 

 amphibolitie schists of the south side ; in the black schists of the 

 Oberalp road on the north side ; sometimes also in the micaceous 

 gneiss of the Gothard massif. Intercalations of limestone always 

 point to an original sedimentary formation of the surrounding 

 schist. A direct proof of this is the existence of rolled gravels in 

 the amphibolic mica schist at 396 m. S. (text to profile, French, 

 p. 52 ; German, p. 48. Geolog. Durchsch., Siidseite, Nos. 55, 56) ; 

 of rolled quartz grains in the sericitic schist (text to profile, French, 

 p. 25 ; German, p. 20. Geolog. Durchsch., Nordseite, No. 64, 68, 

 69, 72, 74, 76, p. 83), and of psammitic quartz rock (talc quartzite ; 

 verrucano ?) between the beds of black schist at 3733, 70, 80, 

 94 m. N. 



The calc-mica schist at the mouth of the Moesa, in the Ticino 

 (pi, X. geol. map along railway), is in a greatly advanced condition 

 of metamorphism, but though changed into calcareous gneiss with 

 accessory disthene, garnets, actinolite, and titanite, and including 

 beds of marble and cipoline, it must be considered as the equivalent 

 of the calc-mica schists of Airolo (tunnel), and of the mica-schist 

 with imbedded calcareous rocks of the Jorio pass (summary profile 

 of the railway on title sheet of the map). 



Continuing the parallelization of the schists on the south side of 

 the St. Gothard with those on its north side, we have to place 

 against the green garnet-mica schists with their intercalations of black 

 gar-net schists, calc-mica schists, and quartzites, the black schists of the 

 Oberalp road with their belongings, and against the felspathic mica 

 schists and amphibolic rocks of the Scipsius (IV. in the scheme on 

 title plate of the map) the slaty gneiss of the north side for which 

 I have proposed the name Ursern-gneiss (see sub-section V.). 



An analogous rock, with striking intercalations of halleflinta, is 

 passed by the railway line near Gurtnellen on the northern flank of 

 the granitic gneiss belonging to the Finsteraarhorn massif (Geol. 

 Map, pi. iii. and title sheet), and southwards from Airolo a corre- 

 sponding gneiss underlies the gray mica schists below Passo Sassella 

 (pi. vi.), and between Monte Piottino (Daziogrande) and Monte 

 Olina (Val Chironico). But amphibolic rocks, which abound near 

 Airolo, are rare or altogether absent in the other localities (Ursern 

 valley, Gurtnellen, Val Chironico). 



III. Dolomite, rauchivacke, marble, cipoline, and subordinate rocks. 

 — The detailed section between 37 and 90 metres from the southern 

 entrance of the tunnel, shown on a scale of 1 : 200 on plate i. of the 

 1 Zeitsch. d. deutsch. geol. Gesellsch, 1879, p. 407. 



