﻿Vol. 64.] AND ANTIGORITE-SERPENTINES. 155 



distant between 17 and 18 miles from Domo d'Ossola. The road, 

 on leaving this town, runs over a stony plain, where also the 

 pebbles gave promise of serpentine, but these were left unexamined 

 for the present ; and, after passing the junction with the Simplon 

 road at Crevola, we entered the beautiful Yal Antigorio. Here 

 and there the road skirts knolls of a variety of gneiss, now com- 

 monly called after the valley: its chief constituents are quartz, 

 white felspar, and rather abundant biotite ; its cliffs and its 

 mode of weathering suggest a granite, with a rather irregular 

 jointing on a large scale, but the rock generally exhibits a fairly- 

 definite cleavage-foliation, and is thus extensively quarried, as in 

 De Saussure's time, to make posts, steps, or flags for roofing, fencing, 

 and paving/ Gradually the sides of the valley become more 

 craggy, and the alluvial plain by the Tosa narrows away on 

 approaching the mouth of the Yal Devero, the torrent from which 

 rushes through a fine, though not very deep, gorge below Baceno, 

 a townlet picturesquely perched on a headland between the two 

 valleys. Beyond this, after passing through Premia, we enter the 

 grander part of the Yal Antigorio, with its magnificent crags, 

 frequent waterfalls, and rich vegetation.^ 



At San Rocco,'^ about half a league below Passo, the bed of the 

 valley (perhaps a quarter of a mile wide from cliff to cliff) is fairly 

 level, and thus boulders and pebble-beds are not unfrequent by the 

 riverside. Here we began our examination, walking up the road 

 for about 3 miles, nearly to E-ivasco, examining the outcrops of 

 rock and the huge fallen masses, now abundant by its side, and 

 making our way at intervals (six or seven times in all, including 

 once just below San E,occo) to promising places by the river. We 

 saw nothing from the road but Antigorio gneiss, and it formed the 

 great majority of the pebbles and boulders, a few being pressure- 

 modified diorites, and a still smaller number a greenish granitoid 

 rock. Kot one was serpentine, from which I infer this rock to be 

 either absent from, or very rare in, the Tosa Yalley above Premia. 



We had now to ascertain the quarter from which the lower part 

 of that valley had received pebbles of serpentine. Early next 

 morning we left San Eocco, and after crossing the Devero torrent 

 came to a spot at the foot of a slope by the roadside, where, on the 

 previous day, I had noticed a few blocks of serpentine (the last 



^ That is to say, it is petrographically a gneiss, but is no doubt a pressure- 

 modified granite. It is very fully described by Dr. S. Traverso in his ' Geologia 

 deir Ossola ' 1895, pp. 59-()9 ; also by Prof. H. Schardt, Archives des Sciences 

 Physiques & Naturelles, ser. 3, vol. xxx (1893) p. 484. 



^ The band of white marble shown in the Swiss map near Premia was not 

 visible by the roadside ; but I found the rock next day both on heaps of road- 

 metal and among the river-pebbles near Domo d'Ossola, nor was the Oberer 

 gneiss with the micaceous variety containing unusually large garnets, of 

 which I got specimens in 1860, at all well exposed (for a description see 

 S. Traverso, op. cit. pp. 49-57). This gneiss differs considerably in aspect from 

 the Antigorio gneiss, and reminded me of one variety common in the Saasthal. 



^ Here, it may be mentioned, the Albergo Yesci affords very fair accommo- 

 dation. 



