GNEISS. 249 



GNEISS. 



THE space occupied by gneiss is often very 

 considerable; and, in many countries, it is found 

 to be the most abundant of the primary stratified 

 rocks, constituting extensive districts, and rising 

 into mountains of great elevation. In such 

 ^ases, it sometimes forms masses of enormous 

 thickness, without any intervening strata of 

 another nature. 



In such situations it is often found imme- 

 diately following granite, and succeeded by the 

 other primary strata. But, as already noticed, 

 it is also frequently observed to succeed one or 

 other of these, or to alternate in large tracts 

 with tracts equally extensive of many of them. 



Besides these more extensive alternations, a 

 large body or series of strata, consisting prin- 

 cipally of gneiss, often contains a number of 

 alternating strata of other rocks in much in- 

 ferior proportion. The most common of these, 



