42 PEOF. T. G. BONNET AND THE REV. E. HILL I [Feb. I912, 



represents an oiFshoot, rather over an inch in thickness, from a 

 dyke in gneiss. Its minerals are as above, but distinctly more 

 irregular in form and size, some felspars being as much as 

 •125 inch in length, while others do not exceed a tenth of this. A 

 fifth example is cut from the indefinite boundary between a red 

 dyke and partly-fused gneiss. The structure, under the microscope, 

 is very irregular, the felspar- grains (of the usual kinds) differ 

 much in size, and it recalls in some parts a dyke, in others the 

 gneiss. 



Fig. 3. — Streaky red and green aplitic rocJc from Oastle Cornet 

 (Guernsey). Natural size. 



SSPMP^l 









An outcrop of the red rock, bounding the side of the above- 

 named little bay, shows two or three irregular patches of a rather 

 compact dark rock, about a yard in diameter, looking like huge ink- 

 spots. In the field we suspected these to be lumps of diorite, not 

 sufiiciently melted to mix appreciably with the other rock (for that 

 is not streaked) ; and microscopic examination of a small fragment 

 shows the darker part to consist of felspar, granular to hypidio- 

 morphic (in which, though decomposed, plagioclase is recognizable), 



