Vol. 50.] GNEISSES IN THE COXXIAN SEQUENCE. 258 



almost vertical, with an E.S.E. strike ; a •well-marked band of fault- 

 breccia here indicates a fault. Thence westward no sections occur 

 on the road until reaching La Balma, where, beside tho mule-path 

 at the west end of the village, there is a crag of the ordinary brown 

 gneissoid mica-schist dipping 42° to 23° west of north. The same 

 schists extend up the Balma Valley to halfway between the conflu- 

 ence of the Balma and the Forcho and the talc-mine at Roussa ; then 

 they recur above the mine, where an amphibolite occurs in them ; 

 they also form the lower slopes of the Rocca Rossa, and thence they 

 can be followed to the south side of the Col Roussa, and southward to 

 the summit of Monte Boeciarda. Near the Alpe di Bocciarda, how- 

 ever, banks of the central gneiss crop up from the pastures, and 

 appear to extend east towards the Punta Sarasina and the 

 Monte Uj a. The actual junction here is hidden by pastures, and an 

 attempt was therefore made to descend to the south in the hope of 

 finding it exposed. The head of the Oomba di Bocciarda is close 

 to the junction, and a small galena-mine may mark the exact 

 position ; owing to the steepness of the descent, however, and a mist 

 that prevented our following the junction, we saw nothing but 

 gneissoid mica- schists, with some amphibolites, till we reached the 

 1300-metre contour. The Roc del Pelvo, which rises above the 

 stream from the base of the great cliff down which we had scrambled, 

 is a sharp pyramid of gneiss and affords clear evidence of intrusion. 

 The foliation of the gneiss dips 45° N.N.E., while the strike 

 is E. 27° S. ; 20 yards from the junction with the gneiss the 

 schists to the north are almost horizontal, but at the contact they 

 are sharply bent upward and are much altered. The gneiss at the 

 junction is impregnated with lines and fragments of dark-coloured 

 included material. Microscopic examination shows that the rock 

 is a normal Waldeusian gneiss. It differs from that described from 

 Bussoleno by the presence of much extraneous matter occurring as 

 lines and rolled-out fragments. Most of the included material is 

 indeterminable, but flakes of chlorite and some rolled, broken, 

 and slightly doubly-refracting garnets may be recognized. The in- 

 clusions farther from the contact are rarer and more altered ; they 

 consist in the main of green and brown hornblende and numerous 

 small garnets ; there are numerous idiomorphic but corroded 

 crystals of orthoclase in the gneiss. The adjoining schists present 

 the same characters as that above the gneiss in the section south of 

 the Chisone ; the rocks consist of bands of chloritic and amphibolic 

 material separated by thin seams of granulite. 



A manganese vein which has been worked occurs along the 

 junction of the gneiss and schists, on both sides of the valley. There, 

 are no slickensided surfaces or other evidence of a fault, and 

 the whole aspect is that of an intrusive igneous mass. This is 

 clearly demonstrated by the contortion and metarnorphism of the 

 adjoining schists, and the inclusions in the gneiss. 



In regard to the possible existence of another bed of intrusive gneiss 

 farther west, between Castel del Bosc and Roure, I am unable to 

 express a definite opinion. Zaccagna arid Mattirolo's map marks the 



