i8a OUTLINES OF I II I I> < ,F,OLOGY PAE1 i 



On the other hand, where the schists have been pro- 

 duced by the metamorphism of an original sedimentary 

 series, they may reproduce some of the more characteristic 

 structural features of stratified rocks. A definite order 

 of succession may be made out among them ; and their 

 groups of qiiarl/iic, limestone, pebbly grit, phyllite, mica 

 schist, hornblende -schist, epidiorite and other rocks 

 may be traceable continuously for long distances. 



FIG. 71. Limestone intercalated among schists and quart/lies Lough Salt, 

 Donegal, a, silvery mica-schist ; b, limestone and dolomite ; c, epidiorite 

 (probably originally intrusive basic igneous rock) crushed in pla 

 hornblende-schist ; d, quartzite. 



Bands of limestone and dolomite are particularly 

 valuable as guides in unravelling the structure of a 

 schistose country. Their line of outcrop can frequently 

 be followed, even from a distance, by the tract of brighter 

 green herbage, supported by the richer calcareous soil 

 which they yield, and contrasting sometimes strongly with 

 the brown moorland on either side. In a cultivated 

 region, especially where the surface is obscured by 

 superficial accumulations, quarries may often be found 

 in the limestone, admitting of an inspection of its char- 

 acter and mineral contents. Limestone bands, moreover, 

 among schistose, as among ordinary sedimentary strata, 



