GNEISS. 251 



Although gneiss is a stratified rock, the se- 

 veral varieties of which it consists, present that 

 disposition in very different degrees. When 

 the texture is coarsely granular, and resembling 

 that of granite, the strata are generally least de- 

 fined ; and, in some such cases, particularly, 

 when it abounds in granite veins, it is difficult 

 for an inexperienced eye to distinguish it from 

 an irregular granitic mass. 



The same difficulty sometimes occurs where 

 it is very irregular in position ; either from a 

 discordant inclination of the approximate por- 

 tions, or from flexures and contortions. The 

 difficulty is in this case increased by the circum- 

 stance that such irregularities prevail most where 

 granite veins are most abundant ; and such is the 

 confusion hence generated, that it often requires 

 an eye of no small experience to distinguish 

 between the vein and the including mass ; or 

 to determine what is granite and what is gneiss. 



Further, the granite veins are not necessarily 

 transverse to the strata or laminae, but often lie 

 in a parallel manner, so as, for short spaces, to 

 resemble portions of the stratified structure of 



