10 Dr. F. M. Stapff—Cfystalline Schists 



graphite ; not only is this the case in this group of the mica-schist 

 series (700 — 800 m.), but also in the following (green schists at 

 1318, 1466, 1808, 1828 m., etc.) and in the black schists of the 

 north side. Garnets are seldom absent, but in the schists close to 

 the dolomites they are small, rare, and sometimes scarcely visible. 

 The second constituent mica is brown magnesian ; it is in part 

 original, in part a pseudomorph, after hornblende. 



Disthene, cyanite, stouroUte (rarely, for example, at 632 and 

 753 m.) occur in certain beds throughout the gray mica schists, 

 whilst they are but sporadic or microscopic rarities in the succeeding 

 green amphibolic and felspathic mica schists. Real staurolite schists 

 comparable with the typical beds of Alpe Sponda have not been met 

 w^ith in the tunnel (text to profile, French, p. 50; German, p. 46) 

 and large radiant prisms of disthene are commonly connected with 

 quartz veins (180, 190, 397 m.), which at the same time carry copper 

 pyrites, pyrrhotine, ironspar and tourmaline (rare). The beds in 

 which disthene and kindred minerals can be recognized at a glance, 

 e.g. at 190, 397, 536, 606, 632, 732, 792, 808, 854, 868, 912, 1119 

 metres from the mouth, are usually connected with the calc-mica 

 schists and black garnet schists; but it would be premature to assert 

 that certain geological horizons in the gray mica schists are charac- 

 terized by the appearance of disthene, etc. 



The complex of gray mica schists containing gai'nets, disthene 

 staurolite (tourmaline), appears again on the opposite side of the 

 Ticino valley (up in the mountains), whence it enters Val Cbironico, 

 with the renowned Sponda Alp ; and it may be seen from the geo- 

 logical map of the railway, plates vi. vii., that even here these mica 

 schists are underlaid by micaceous gneiss and overlaid by real calc- 

 mica schists, with intercalations of black schists, quartzites, and 

 (last but not least) by dolomites, rauchwacke, marble, etc., in 

 repeated beds. 



The so-called calc-mica schists of the Gothard tunnel (south side, 

 text to profile, French, p. 50; German, p. 45) differ to some extent 

 from the calc-mica schists on the opposite side of the Ticino valley ; 

 the calcspar being scarce and often absent in the rusty outcrops of 

 the small seams ; which are then hardly recognizable as con- 

 tinuations of the corresponding calcareous mica schists in the tunnel 

 (pi. V. of the geological map along the railway line). The calcspar 

 usually occurs together with quartz or felspar, in thin crumpled, 

 broken and faulted lamellae, which by the decomposition of pyrites 

 or carbonate of iron are often rusty and carious. Some quartzitic 

 beds of this mica schist series and some amphibolites (liemithrenes) 

 also yield grains and lamellae of calcspar, and it would be interesting 

 if there were means of distinguishing the original constituent from 

 the secondary calcspar, so as to be able to decide whether these 

 intercalated seams are real or pseudo calc-mica schists. With regard 

 to their designation in the profile of the tunnel, I refer to the 

 remarks made above respecting the black garnet schists. 



Certain seams of the sericitic schists of the Ursern valley (north 

 side) are also calcareous (3255-85; 3560-70; 3650, 3666 m. N., 



