A^^'XIYERSAET ADDEESS OF THE PRESIDENT. 73 



then Lias slate, followed by raucliwacke, and then by gneiss. The 

 melanite schist, as I shall presently show, is undoubtedly much less 

 ancient than the gneiss ; the position of the rauchwacke is uncertain, 

 but I consider it, not as associated with the melanite schist, but as of 

 much later, probably of Mesozoic age. It is obvious that in any 

 case we have here a region folded and possibly faulted in the most 

 extraordinary way. 



The rauchwacke occupies much of the open basin which forms 

 the upper part of the Lukmauier pass. Fiom. this the road descends 

 to Olivone, along a valley roughly running E.S.E. ; but in order to 

 ascertain the relation of the rocks on the southern slope of the 

 watershed, it will be better to turn aside in a Yv^'.S.W. direction and 

 examine the ground between Santa Maria and the Yal Bedretto. 

 From Airolo, at the foot of the descent from the St. Gothard, to the 

 top of the Lukmauier pass, as may be seen on the Swiss geological 

 map, a zone extends, occupied by a variety of schists of a well- 

 marked mineral character, together with some rauchwacke. These 

 rocks cross the lower part of the noted Yal Canaria, form the right 

 bank of the Lago de Ritom, and then running almost due east 

 crop out along the upper slopes on the southern side of the Luk- 

 mauier Pass. Prom Airolo to a spot about 3| miles E. of Lake 

 Ritom (a distance of some eight miles in all) this trough is 

 bounded on its northern face by mica-schists, among which the 

 peculiar actinohtic and garnet-bearing schists (Tremola schists)* 

 already mentioned are predominant. A gneiss, which hitherto has 

 formed the northern boundary of the latter schists, then sets in. 

 The southern boundary of the trough (which is mapped as a kind 

 of peninsula from a much larger mass occupying the mountain 

 region on the south side of the Yal Bedretto) is formed by gneisses, 

 which, like the above mentioned, are commonly rather micaceous ; 

 in these also I have seen (though rarely) calcareous bands. The 

 gneiss on the northern side of the trough, speaking inclusively, is 

 an extension of that dominant on the northern slope of the St. 

 Gothard ; that on the southern side may also be fairly regarded as 

 an extension of the same rock. I account for the absence of the 

 Tremola schists by faulting, probably upthrust. This idea, the 

 structure of the gneiss itself, indicating great compression at a high 

 angle with the apparent bedding, fully confirms. 



Neglecting the rauchwacke, which I regard as a rock of com- 

 paratively late date, I turn to the schists which occupy a part of 

 the above-named trough in the Yal Piora, and occur to the south 

 of the Tremola schists. The highest (not in geographical position) 

 is a series of black mica-schists with melanite, interstratified with 

 a light brown felspathic quartzite. Beneath this comes a zone c 

 rather silvery mica-schist, with beautifully developed staurolite 

 crystals, ove dying a thick bed of quartzite. These appear to be 

 followed by a series of variable schists, some quartzose, some cal- 

 careous, all containing more or less of a silver}' mica, probably 



* These schists can be traced some few miles at least further west, up the 

 Val Bedretto. The Swiss map gives them a total extension of about 13 miles. 



