GNEISS. COMPACT FELSPAR. 143 



tindulatirig deviation, both from the line of direction 

 and the angle of the dip, which exists in all the primary 

 strata. But this regularity prevails chiefly in the 

 schistose variety; while the granitic one is distinguished 

 by the frequency and extent of its flexures and contor- 

 tions, generating that irregularity, just noticed, which 

 is so characteristic of this variety and so explanatory of 

 the theory of gneiss. These are often such, that it is 

 impossible to assign either the dip or direction of the 

 strata ; while often producing the appearance of two 

 se\s with opposite dif>s, when the one is only a portion 

 of the other, incurvated, or doubled on itself. In other 

 cases., they are diposed in a lengthened undulating 

 manner, either horizontally or vertically, or in larger 

 curves resembling the waves of a sea, sometimes again 

 interrupted by straight portions. The cliffs of the Long 

 Island present natural sections of all these forms, de- 

 tailed as in a drawing ; with abundant other examples 

 of contortions so intricate and capricious, that the ima- 

 gination can scarcely exceed them. 



Gneiss is so frequently traversed by veins of granite, 

 that they may almost be esteemed characteristic of one 

 of its varieties; while they occur in the other less con- 

 spicuously, and, in some of its connexions, only as they 

 do in the primary strata in general. They are of all 

 sizes, from the thickness of many hundred feet to that 

 of less than an inch ; being either simple, or ramifying, 

 even to extreme minuteness, and interectingeach other 

 in all modes ; as they also traverse the rock in trans- 

 verse directions or in that of the laminae ; while, as might 

 be expected, this last appearance prevails in the schis- 

 tose variety. As I just hinted, these veins are most 

 abundant in the granitic kind; while, being more rare 

 in the schistose, they generally disappear altogether as 

 its texture approaches to that of micaceous schist. 



