Vol. 50.] GNEISSES IN THE COITIAN SEQUENCE. 241 



1892 Dr. Gianotti 1 and Prof. Chelussi 2 have added considerably 

 to our knowledge of the south-eastern corner of the massif. From 

 the works of these authors we know that the main part of the massif 

 consists of a coarse augen-gneiss which passes into a granite at the 

 centre and becomes finer grained around the margin; it is surrounded 

 by schists, which are often intensely contorted and penetrated by 

 a series of gabbros and ' pietre verdi.' Near the gneiss the strike 

 both of the schists and greenstones is as a rule parallel to the margin ; 

 and the maps show the beds of ' pietre verdi ' and limestone in the 

 schists encircling the gneiss, in a manner which suggests that their 

 strike is due to uplift around a; central intrusion. Gastaldi admits 

 that the ellipsoid of elevation of the Paradiso is due to the intrusion 

 of the gneiss, but he maintains that this was in a solid state, 3 and 

 this is apparently accepted by most Italian geologists, Gastaldi, 

 however, in the map previously quoted, of which part is here 

 reproduced (see fig. 2), has shown one band of the ' pietre verdi' com- 

 pletely broken across by the gneiss in a manner that appears almost 

 inexplicable for a solid intrusion. Though not inclined to place 

 much reliance on Gastaldi's mapping, I thought it advisable to select 

 this area for the examination of the relations of the gneisses and 

 schists. A further advantage offered by this part of the massif 

 was that the line of junction of the two had recently been precisely 

 marked on a map to the scale of 1 : 25,000, issued by Dr. Gianotti 

 in illustration of his paper on the mode of formation of the valleys 

 around Chialamberto. 



The central gneiss has been so well described macroscopically by 

 Baretti 4 and microscopically by Chelussi 3 that there is no need 

 here to say more than that around the margin it is typically a 

 coarse augen-gneiss with felspar ' eyes ' often 2 inches in diameter, 

 and with all the minerals remarkably fresh. 



In the centre of the massif the gneiss, as we are told by Baretti 6 

 and Gianotti, 7 passes into a normal coarse-grained granite, without 

 any trace of foliation. At the actual contact with the surrounding 

 schists the gneiss becomes much more finely foliated and the large 

 felspar 'eyes' disappear. The junction, however, is unfortunately 

 generally covered by moraine, and actual contact is rarely to be seen. 

 Above the level upland valley, on the lower edge of which stands 

 the hamlet of Vonzo, the stream of the same name runs for some 

 distance along the line marked on Dr. Gianotti's map as the junction 



1 G. Gianotti, 'Appunti geologiei sulla Valle di Chialamberto' (Valle di 

 Lanzo— Alpi Graie), Boll. Soc. geol. Ital. vol. x. (1891) pp. 149-167. 



- I. Chelussi, ' Studio microscopico di alcune roccie della Valle di Chialam- 

 berto in Piemonte,' pt. i. Giorn. Min. Crist, e Petrogr. vol. ii. (1891) pp. 196- 

 210; pt. ii. ibid. pp. 270-277. 



3 Gastaldi, Mem. descriz. Carta geol. Italia, vol. ii. (1874) p. 58. 



4 Baretti, ' Gran Paradiso,' Atti E. Acead. Lincei, ser. 3, Mem. vol. i. pt. i. 

 (1877) pp. 208-211. 



5 Chelussi, op. supfa cit. pt. ii. Giorn. Min. Crist, e Petrogr. vol. ii. 

 pp. 270, 271. 



6 Baretti, he. supra cit. 7 Gianotti, op. supra cit. p. 153. 



