OVERLYING ROCKS. 497 



both in veins and in masses. In some cases, it 

 contains crystals (or grains) of two colours, as 

 white with dark lead blue, or greyish green with 

 blackish green or lead blue, and has then been 

 confounded with the greenstones. This might be 

 called a pseudo-greenstone. In other cases it 

 presents various simple tints, like the preceding 

 varieties. It seems doubtful whether this variety 

 does not sometimes consist of an aggregation of 

 common instead of compact felspar. 



Fawn and cinnamon colours are found in var. 

 a, b ; but they also occur of a brick red hue, of 

 a muddy white, arid of every possible tint of 

 grey down to nearly black. There seems to be a 

 gradation from clinkstone to compact felspar, as 

 there is between the varieties C, D, . 



The simple compact felspars pass into por- 

 phyry so commonly, that it is not easy to find an 

 extensive mass absolutely free from imbedded 

 crystals. Hence a specimen is not a criterion of 

 the nature of an extensive rock. 



A similar remark may be made, generally, on 

 the four varieties C, D, E, F ; which, although 

 simple in one place, may be porphyritic or amyg- 



K K 



