Washington — Study of the Glaucophane Schists. 43 



and somewhat silky luster. Under the microscope they corre- 

 spond with the plate given by Teall*, and are seen to be 

 composed of a rather pale, prismatic glaucopbane, with the 

 normal pleochroism, rather less pale epidote, and small 

 amounts of magnetite, quartz, mica and titanite. !N"o calcite 

 was seen. 



Piedmont. 



The occurrence of glaucophane schists in Piedmont is well 

 known, and has been described by many geologists, but as I 

 had no specimens from this region, I have passed it by in the 

 preceding pages. Since they have been put in type, however, 

 I have discovered an analysis of one of the rocks of this region, 

 which is inserted here. 



The occurrence of glaucophane schists and amphibolites 

 (" prasinites ") in the Yal Maira, in southwestern Piedmont, is 

 described by S. Franchi, f who also shows that they are both 

 derived from diabases by metamorphism, apparently regional. 

 The glaucophane schists are described as composed of glauco- 

 phane (gastaldite), with epidote and chlorite, and less albite, 

 quartz, titanite and calcite. Analyses of this and of the amphi- 

 bolite are given, and the very close correspondence between 

 the two is evident. This is a strong point in favor of the view 

 elsewhere expressed, that the formation of these two rocks is 

 due, not to age distinctions, but to differences in conditions 

 during metamorphism. 



I. II. 



Si0 2 48'67 50-38 



A1 2 G 3 18-36 17-65 



Fe 2 3 10-30 10-02 



FeO 



MgO 5-49 4-77 



CaO 11-03 10-95 



Na 2 G 1-12 2-52 



K 2 0-11 0-24 



H 2 4-20 2-52 



Ti0 2 0-45 1*32 



P 2 5 .. trace trace 



99-75 100-37 



I. Glaucophane schist, Val Maira, Piedmont. Aichino anal. 

 S. Franchi, Boll. Com. Geol. Ital., xxvi, p. 199, 1895. 

 II. Amphibolite (" Prasinite "), Valle del Sangone, Piedmont. 

 , Aichino anal. S. Franchi, op. cit., p. 199. 



Corsica. 

 For the sake of completeness there may be mentioned two 

 glaucophane rocks of Corsica, which have been analyzed. 



*Teall, Brit. Petrog. 1888, pi. xlvii, fig. I. 



fS. Franchi, Boll. Com. Geol. Ital., vol. xxvi, p. 192, 1895. 



