CHAPTER XIII 



SCHISTOSE ROCKS MINERAL VEINS 



A GEOLOGIST who, with some little experience of strati- 

 fied and igneous rocks, finds himself for the first time in 

 a region of crystalline schists, meets on every hand with 

 phenomena, which, though he may be familiar enough 

 with the descriptions of them in books, cannot but strike 

 him as strangely anomalous when he comes actually face 

 to face with them in nature. The rocks are manifestly 

 crystalline, and in small fragments or hand -specimens 

 may often recall some of the igneous rocks with which 

 he may already be acquainted. But when looked at 

 in mass, they have an arrangement of their component 

 minerals such as he probably never observed in any 

 igneous rock. The felspars, hornblende, quartz, mica, 

 and other constituent minerals, are disposed in more or 

 less regular wavy lines, and the rock splits along these lines 

 more readily than in other directions. Again, so distinct 

 sometimes are the parallel seams of different mineral 

 composition, that the rocks might at first be mistaken for 

 ordinary sedimentary strata. Yet a little further examina- 

 tion shows that the layers or folia are welded or felted 

 into each other by the interweaving of their crystalline 



