242 



DR. J. W. GREGORY ON THE WALDENSIAN [M.ay 1 894, 



of the two series ; no exposure of this can be here seen in situ, hut 

 some of the boulders on the banks and in the bed of the stream do 

 show the actual junction. 



Fig. 3 shows one of these cases : the boulder consists of a mass 

 of fine-grained gneiss including two masses of the ' pietre-verdi ' 

 series ; the foliation of the gneiss flows round the inclusion, which 

 shows clear contact-alteration to a depth varying between j and | 

 inch. The gneiss is finer in grain than any we could find there in situ, 

 but other boulders showed a passage from gneiss having characters 

 identical with this to the normal coarse-grained rock. Microscopic 

 examination completely demonstrates that the gneiss belongs to the 

 central mass. Half an inch from the contact the gneiss is clear 

 and colourless, and all the minerals are remarkably fresh ; the main 

 mass of the rock is formed by a water-clear quartz-felspar mosaic, 



Fig. 3. — Inclusion of ' pietre verdi ' in the gneiss of the Vonzo Vallejf. 



[Reproduced from a photograph.] 



the constituents of which are often united in pegmatitic inter- 

 growths. The quartz has a well-marked circular polarization ; the 

 orthoclase is occasionally idiomorphic, and Carlsbad twins occur; 

 these crystals also show signs of corrosion. Oligoclase occurs only as 

 a few rounded grains. The mica is white and occurs in long blade- 

 like crystals, most of which lie along the planes of foliation ; a 

 few, however, are scattered irregularly through the quartz-felspar 

 mosaic. 



