394 MR. ¥. RUTLET ON ERI7PTIVE -ROCKS FROM THE 



strings, some of which (opaque white) are cut off by, while others- 

 (rusty-coloured) traverse the vein. 



Fig. 1. — Cant Eill, East end, at top of hill. 



a a. Greenish-yellow to brownish -yellow scaly serpentinous matter. 



The sketch shows the continuity of bands of this serpentinous substance with 

 the cross vein of the same material. In the vein the scaly character is better 

 Been than in the bands, since in the vein the scales lie confusedly in all directions, 

 while in the bands they are approximately parallel. 



In the felsitic portions of the preparation numerous small circular 

 and lenticular spaces occur, filled sometimes with quartz and at 

 others with serpentine. These have apparently been vesicles, and 

 from these, and from the appearance of fluxion-structure, there 

 seems little doubt that the rock was originally a lava. In one or 

 two places there seems to be evidence of a banded, and perhaps 

 spherulitic structure, as shown in the middle of fig. 1, Plate XII. 

 We have now advanced far enough in our examination to assume 

 that we are dealing with a banded vesicular lava. The next point 

 to ascertain is the nature of the assumed lava. 



Porphyritic felspars are present in tolerable quantity, but they 

 are often considerably altered. Where they are sufficiently fresh 

 to exhibit distinct optical properties they are seen, from their extinc- 

 tions, to be triclinic, the extinction-angles often approximating to 

 those of labradorite. The next point of interest is the profusion of 

 serpentine which is present in the rock. It occurs chiefly in 

 irregular or lenticular patches which fade away into filaments, 

 granular specks, or stains. The general appearance, however, is 

 that of very irregular bands, and it seems probable that their more 

 expanded portions represent pseudomorphs after pyroxene or olivine 

 which have been reduced to lenticular forms by pressure. The 

 opaque rusty-coloured matter in the rock is limonite ; the opaque 

 white substance kaolin, or perhaps leucoxene in part. We have 

 therefore, with the exception of a few imperfectly altered crystals of 

 triclinic felspar, nothing but decomposition-products. If from these 

 secondary materials we endeavour to speculate on the original 

 mineral constitution of the rock, we have triclinic felspar (labradorite 



