142 GNEISS. COMPACT FELSPAR. 



most undistinguishable from the quartz, except by its 

 decomposition on the weathered surfaces; this variety 

 is frequently confounded with one or other of the rocks 

 above mentioned. The laminar division is more rare, 

 and of little geological interest ; being distinguished 

 by the laminar alternating disposition of its ingredients; 

 and the specimens often exhibiting singular combina^- 

 tions of colour. The last division is characterized by 

 the presence of compact felspar. I need here only add, 

 that the topaz rock of the Germans is merely an acci- 

 dental modification of this rock ; as the weissstein ap- 

 pears also to be, unless this be, sometimes, a granite. 



The stratification of gneiss is unquestionable, how- 

 ever difficult it may sometimes be to determine its order, 

 or even to perceive its existence. In Scotland, where 

 this rock abounds, the prevailing direction of the pri- 

 mary strata is between the N. E. and the N. N. E.; 

 and, while it conforms to this when obvious, there are 

 indications in the bearings of the coast, the positions 

 of the hills, or the comparison of parts on a greater 

 scale, which prove, that even where most obscure, it 

 follows the same leading line. It is often, in fact, by 

 this prevailing conformity alone, that the stratified dis- 

 position of gneiss is perceptible ; since, its irregularity 

 is often such, and the indication of beds so obscure, 

 that it is as easily confounded with granite by its dis- 

 position as its mineral character. It will shortly be 

 seen, that its characters as to regularity, are connected 

 with its peculiarities of structure ; one of the leading 

 mineral divisions being irregular, while the other equals 

 in this respect the accompanying strata. It is super- 

 fluous to say that every possible variety of dip occurs 

 in this, as in all the other primary strata. 



The beds of gneiss are often straight, or even ; or, 

 at least, affected by no further irregularities than that 



