THE MATERIALS OF MOUNTAIN CHAINS. 23 



crystallization which has blended the grains. In 

 some localities, as on the west coast oi Scotland, 

 limestone occurs in schists and gneiss. Its tex- 

 ture is frequently compact and crystalline, and 

 sometimes saccharoid like statuary marble. It 

 contains many minerals but no fossils. All lime- 

 stones were originally deposited from water. 

 Thus the three chief types of water-formed rock 

 — sandstone, Clay and limestone — appear to be 



represented among 5, The process which 



has rendered them crystalline is termed metamor- 

 phism. Metamorphic rocks, which divide into 



layers by differences in the mineral character of 

 their crystalline constituents, are said to be foli- 

 ated. This foliation may be regarded as closely 



comparable with the cleavage of slates. 



Schi>t> may be formed of quartz, felspar and 

 mica in parallel layers, when the rock is termed 

 -v. Th f a schist may be thrown 



out of their parallelism, as in Anglesea, 50 as to 

 present a confused mixture, which has been 

 termed granite. Some >, however, take 



the converse view, and believe that the original 

 ire of the rock was granite, and that the 

 schistose texture has been acquired by shearing 

 movement acting on a heated plastic rock. In 

 the south of Cornwall a schistose texture has 

 been imparted in the metamorphic region of 

 Cornish schists, to rocks which were originally 

 volcanic. 



Metamorphism is produced in several distinct 

 ways. When the rocks of an elevated tract be- 

 come changed in texture throughout their mass, 

 the expression " regional metamorphism " has 

 been used to distinguish such wide-spread trans- 

 formations of rock texture, from the local altera- 



