BV LEO A. COTTON. 



769 



of this decomposition-product in connection with the lodes is, I 

 think, very significant, and of genetic importance. The lodes of 

 Cornwall frequently present the same characteristic. The veins 

 of quartz intersecting the felspathic lode-material often pass into 

 felspar or cassiterite, while still preserving the same width. 

 Text-fig. 5 illustrates this. 



One curious case was observed in which the cassiterite arranged 

 itself in two parallel planes, each entirely in the felspathic lode- 



nches 



Fig- 5. Fig. 6. 



Fig. 5. — Portion of quartz-felspar lode, showing how the quartz-vein may' I 

 pass into cassiterite or the felspar of the lode. Q, Quartz; C, Cassiterite; 

 F, Felspar. 



Fig. 6.— Section of quartz-felspar lode, showing peculiar disposition of 

 cassiterite. Q, Vein-quartz; C, Cassiterite; F, Quartz-felspar lode-material. 



material, and about an inch distant from the central seam of 

 quartz(see text-fig. 6). 



(ii.) A number of lodes occur, which consist of a very intimate 

 quartz-felspar mixture, the latter mineral predominating. In 

 these, cassiterite, where it does occur, is distributed with a fair 

 degree of uniformity. No bands or seams are to be seen, but it 

 occurs as a constituent of the rock (see Plate Ixii., fig. 2). These 

 lodes are frequently very soft and, as in the first group, the 

 country-rock is soft and decomposed. In any particular lode 

 much is quite barren, the cassiterite occurring in rich patches. 



