278 Canadian Record of Science. 



the present the arm-like extension and that part of the 

 main area adjacent to it, it will be noticed that the rock 

 which is coarsely granular and of a deep violet colour, 

 has not the regular structure which we find in a typical 

 granite, but exhibits- a more or less irregular structure. 

 At times this is scarcely noticeable, but at other times it 

 is very distinct, and is due to the fact that the bisilicates 

 and iron ores are much more abundant in some parts of 

 the rock than in others. The portions richer in bisilicates 

 form either very large irregularly-bounded spots, which 

 appear here and there, or a large number of small spots. 

 In some cases they occur abundantly in the rock, while in 

 others they are entirely wanting. The coloured portions 

 are sometimes so arranged that instead of irregular spots 

 they form undulating stripes, whose direction is sometimes 

 sufficiently continuous to give a kind of strike to the rock. 

 In other cases, however, they are irregular. Between 

 these spots or stripes, which are comparatively rich in 

 bisilicates, and badly defined against them lies the chief 

 mass of the rock. It contains only very little and some- 

 times even no bisilicates, and in it there lie large broken 

 crystals of plagioclase, often heaped up in certain places 

 or especially numerous in certain directions. In intimate 

 connection with this irregular distribution of the constitu- 

 ents of the rock, and 

 sometimes also quite 

 independent of it, 

 there occur local vari- 

 ations in the size of 

 grain which are like- 

 wise exhibited in spots 

 or stripes. Theaccom- 

 Fig. i. panying drawing (see 



Fig. 1), made from a photograph, represents a weathered 

 surface of a variety which is unusually rich in coloured 

 ingredients. An irregular structure produced by one or 



