218 GENERAL REMARKS ON GNEISS. 



The stratified disposition of gneiss, and its conformity 

 to the general bearing of the Scottish strata, have 

 already been noticed. The causes of the obscurity 

 which occasionally attends it must also have been 

 apparent ; but it may be added that this obscurity is almost 

 peculiar to the granitic variety, and that the schistose 

 is generally disposed with as great a degree of regularity as 

 the analogous rocks, micaceous schist, quartz rock, and 

 clay slate. It is scarcely necessaiy to repeat, that 

 every possible variation of dip is combined with this 

 uncertainty of direction. The flexures present an endless 

 variety, and, like the other irregularities, are almost 

 limited to the granitic division. They have been fully 

 described where they occurred. 



All the varieties of gneiss are occasionally intersected 

 by granite veins, and they are indeed almost characteristic 

 of this rock ; being rarely absent for any considerable 

 space, and seldom traversing micaceous schist unless 

 under circumstances where they can be traced to some 

 neighbouring mass of granite. They are however most 

 abundant in the granitic division. They are infinitely 

 various in size and in the number and intricacy of 

 their ramifications ; and it is further worthy of remark, 

 that the contortions of any mass of gneiss are always 

 proportioned to the number and importance of those 

 which it contains.* Hence it is that the schistose 

 is more free from contortions than the granitic variety. 

 It is nevertheless proper to make an exception 



* As almost every part of Scotland presents examples to illustrate 

 this remark it is unnecessary to quote the places where they occur. 

 But the gneiss of Strontian offers an instance too important to pass 

 unnoticed. The whole of the surrounding country is formed of beds 

 holding a rectilinear course and presenting an undisturbed stratification, 

 while they contain very few granite veins. But in the vicinity of the 

 granite of that district the veins become numerous, and here the re- 

 gularity of tl\e gneiss ceases, while it also assumes a character more 

 decidedly granitic. 



