76 TRANSFORMATIONS OF ROCK-MATTER. 



daily see in the manufacture of the metals, glass, and earth- 

 enware. Such, we repeat, are the more general and likely- 

 causes of rock-metamorphism ; and as it is possible that 

 several of these may be operating within the same locality 

 at the same time, the reader will perceive that no hypo- 

 thesis that limits itself to any one agent can be accepted 

 as sufficient and satisfactory. 



It has been already stated, that while every stratum 

 or portion of a stratum, every formation or portion of a 

 formation, may undergo metamorphism, it was to the older 

 and deeper-seated slates and schists that the term Meta- 

 morphic was more especially applied it being chiefly 

 among these that mineral transformations were to be wit- 

 nessed in their greatest intensity. It is true that in many 

 secondary mountains, such as the Alps and Apennines, the 

 stratified rocks are often highly metamorphosed ; but this 

 transformation is for the most part partial, some localities 

 remaining little affected, and having all their fossils distinct 

 and legible. Near one centre of vulcanic energy the shales 

 may be converted into dark glistening schists and the 

 limestones into crystalline marbles, while in another cen- 

 tre, and only a few miles distant, the shales and limestones 

 may retain their original sedimentary aspect. Among the 

 primary formations, on the other hand, the metamorphism 

 is general, and whole mountain-ranges and vast tracts of 

 country, like the Scottish Highlands and Scandinavia, are 

 entirely composed of crystalline slates and schists the 

 clay-slates, mica-schists, chlorite-schists, gneisses, quartzites, 

 marbles, and serpentines of the mineralogist. Among 

 these rocks stratification is indistinct, fossils are obliterated, 

 and the whole succession is massed into one enormous 

 thickness of unknown origin and antiquity. Under this 

 view these rocks have been successively regarded as 



