Vol. 50.] THE WALKENSrAN GNEISSES. 239 



series. In regard to the gneiss, however, Prof. Bonney twice sug- 

 gested, 1 from microscopical examination, that it is " not impossibly 

 of igueous origin ; " but lie insisted on the remarkable coincidence 

 between it and the Laurentian gneisses. 2 



Dr. Dinner, in the admirable summary of the subject in his ' Ge- 

 birgsbau der Westalpen,' accepts (pp. 15, 16) the same threefold 

 sequence ; but he remarks (p. 33) that the evidence for Zaccagna's 

 anticlinal is not conclusive, and shows that part of the ' schistes 

 lustres, 1 though in another district, are certainly Triassic. 3 



The work of both Zaecagna and Bonney was executed on the 

 passes ; failure, however, on previous occasions to obtain sufficiently 

 satisfactory exposures on the closelv cultivated, moraine-strewn 

 flanks of the valleys led me to trust mainly to the peaks and 

 ridges and to follow the strike from north to south, in the hope of 

 thus Hading a series of clear exposures of the junctions. 



III. The Gneisses. 



Zaecagna, in the exquisite map attached to his memoir ' Sulla 

 Geologia delle Alpi occidentali,' figures the gneiss as a continuous 

 band from Bussoleno to Venasca, a distance of some 80 kilometres or 

 50 miles. I had, therefore, planned to start at the north end, work 

 steadily south along the western margin of the gneiss, and return 

 north along the eastern margin. The first day's work, however, 

 showed that no such simple scheme as this was practicable. The 

 gneiss ma}' be found a short distance south of Bussoleno, forming a 

 low bank, ranging along the base of the hills, below the villages of 

 Fornielli and Combe ; but on attempting to work south along the 

 line of junction marked by Zaecagna, one soon left the gneiss and 

 struck a wide stretch of mica-schists, with calc-schists on the north- 

 western border. At two or three places to the south there are small 

 exposures of dykes or banks of the gneiss, but we could find no 

 trace of the great sheet of gneiss which Zaccagna's map had led 

 us to expect. All along the line, the results were much the same; 

 instead of the continuous band of gneiss, there appears to be really 

 a series of disconnected masses. This is the case not only in the 

 Bussoleno district, but as far south as the line of gneisses was 

 followed ; it is shown in the map of Vasseur and Carez, which in 

 this respect appears to be more accurate than Zaecagna and Mat- 

 tirolo's map. It seems, therefore, best to discontinue the use of 

 the term ' central gneiss,' which has been applied in the area to 

 many different rocks and moreover assumes the point in dispute. 

 But as the gneisses are mainly exposed in the Waldensian valleys 

 they may be appropriately called the ' Waldensian gneisses.' They 

 may be divided into seven groups, each of which is perhaps best 

 described separately : — 



1 Quart. Journ. Geol. Soc. vol. xlv. (1889) pp. 83 and 99. 



2 Ibid. p. 97. 



3 Such is the case around Lago Paroird and Mont Brise, ' Gebirgsbau der 

 Westalpen,' p. 103. m 



