of the. Lejjontine Alps. 17 



Explanation of Autotype Figures on page 16. 

 Microscopic sections of micaceous limestone from the St. Gothard tunnel, showing 

 traces of organic structures. Reproduced by Autotypic process. Enlarged to 

 the scale of 180 diameters. The upper one is from Bed No. 43; the lower 

 from Bed No. 45. ^ 



mained the groundwork for the subsequent classifications published 

 in the geological profile of the tunnel (1880), and in the title sheet 

 of the geological map along the railway line (1885). The summary- 

 profile between the Lake of the four Cantons and that of Lugano, as 

 there delineated on the scale of 1 : 250,000, afi'ords an insight into 

 the structure of the Lepontine Alps which differs materially from 

 others drawn up before the construction of the tunnel. Space would 

 not permit me to give detailed references to this profile, and I 

 shall therefore restrict myself to a sketch of the classification of the 

 crystalline schists for which I wish to maintain my priority. 



1. The micaceous gneiss with predominant magnesian-mica, which 

 in the central part of the Gothard massif occupies the Guspis valley 

 between Greno di Prosa (dividing ridge of the St. Gothard) and 

 Alpetligrat, and extends in the tunnel for a distance of 2270 metres, 

 from 5450 m. S. to 7200 m. N., is the oldest or deepest of the crystal- 

 line schists of the St. Gothard, and as such is marked by J; Guspis 

 glimmergneiss. One peculiarity of the same beds is the occurrence 

 of black tourmaline together with garnets. Gneissic, micaceous, 

 amphibolic, and quartzitic varieties, exist in it, as well as in the 

 succeeding groups, and they have been carefully set out in the Geol. 

 Durchsch. (1:200), and summarily in tlie profile of the tunnel, not 

 only for engineering purposes, but also to serve as marks for the 

 identification of crystalline strata on either side of the mountain. 



The presence of rolled quartz grains (sand) in some beds of the 

 -Guspis micaceous gneiss, which have been duly noted in the Geol. 

 Durchsch. (for instance No. 130 N. at 7262 m. p. 178, 9), and in the 

 text to the geol. profile (German, pp. 28, 31, 36; French, pp. 31, 

 34, 39), proves beyond doubt the original sedimentary character of 

 this gneiss, and this view is corroborated by the occurrence of 

 occasional small bands of limestone (at 6100 — 6110, 7352 N.), fre- 

 quently containing microscopic globules of graphite or other coaly 

 material.^ As a consequence, all the succeeding crystalline schists 

 of the St. Gothard must also be considered to be metamorphosed 

 sediments, so far as they cannot be shown to be of plutonic origin. 



2. The Sellagneiss, southwards of the micaceous Guspis-gneiss 

 and the Gamsboden-gneiss (a term introduced by v. Fritsch) north- 

 wards of it, occupy the second horizon of the crystalline schists, 

 which is marked by II. I consider them equivalent to the Ticino 

 gneiss south of the St. Gothard, which is crossed by the railway line 

 between Daziogrande and Claro, and noted on pis. vi. — x. of the map 



1 As already mentioned by Prof. Bonney {loc. cit. p. 198) hand -specimens of these 

 St. Gothard rocks are preserved in the Mineralogical Collection of the British 

 Museum (Natural History), and sections, taken from the one marked No. 43, show 

 precisely similar structures to those in the accompanying figure. — Edit. Geol. Mag. 



* There is no question here about graphitic mirrors on fissures. 



DECADE III. VOL. IX. NO. I. 2 



