298 SKY. GEOLOGY. GNEISS. 



these, each substance that enters into its composition 

 forming a separate lamina more or less extensive. No 

 granite veins are to be seen, or, if they exist, they are 

 rare, since none occurred throughout a very extensive 

 and minute examination. I have formerly attempted to 

 show that the contortions and irregularities of gneiss 

 were accompanied by the presence of granite veins : the 

 present example seems to confirm that view, while it also 

 proves that they are not necessary to its constitution. 



The predominant feature in the composition of this 

 gneiss, is the abundance as well as the distinctness and 

 red colour of the felspar, which is seldom entirely absent^ 

 even from those accompanying rocks of other characters 

 that will hereafter be described. In the greater number 

 of instances it is interlaminated chiefly with quartz ; mica 

 entering into the structure in very small proportion, 

 and commonly occupying a distinct and thin lamina. 

 In some cases the mixture is more confused, but gene- 

 rally the mica is even then in very small quantity. 

 This variety of gneiss has a very peculiar appearance, 

 from the contrast of the red and white colours ; and, where 

 the laminae are even, it forms a beautiful rock. 



The next variety consists of chlorite schist, felspar, and 

 quartz, and here it may be a question whether, mine- 

 ralogically considered, such a compound ought to be 

 called gneiss. In the meantime, from the want of another 

 name, from general similarity of character, and from the 

 nature of the transition by which it passes into genuine 

 gneiss, it may be allowed to stand as a variety of that 

 substance.* In fact it is no further distinct than are 

 the varieties so abundant in the Long Isle that contain 

 hornblende in lieu of mica ; which have without scruple 

 been ranked by geologists under the same term. These 

 occur also in Sky, and, commonly, more or less intimately 

 associated with the beds of hornblende schist that alternate 

 with the gneiss. 



* I have already so arranged it in the Synopsis of Gneiss. 



