317 



QUARTZ ROCK, 



THIS important member of the primary strata 

 has been long known to geologists, but had 

 never been thoroughly understood until it was 

 described in a succession of papers published in 

 the Transactions of the Geological Society. An 

 abstract of these was afterwards introduced in the 

 " Description of the Western Islands," to which 

 work the reader may be referred for a fuller ac- 

 count of its geological characters. 



Quartz rock, like the primary rocks with 

 which it is usually associated, is stratified ; the 

 distinction of the beds being however much more 

 strongly marked than they are, either in gneiss 

 or micaceous schist, and very commonly as well 

 defined as in the secondary sandstones. They 

 vary exceedingly in dimensions, even from an 

 inch to many yards in thickness ; and as they 

 often possess natural joints, they break, like many 

 of the schistose rocks, into rhomboidal orrectan- 



