GNEISS. 153 



Vaded gneiss is not only disturbed, but assume these 

 character of the accompanying granite. If exceptions 

 occur, they depend, like all others, on collateral cir- 

 cumstances generally easy of explanation, but requiring 

 a particular one for each case. I need only further 

 repeat, that the alternations of gneiss and hornblende 

 schist present a very exact analogy to those of sand- 

 stone and shale; while as the latter are converted into 

 hornblende schist and basalt by the action of heat, it 

 is easy to see how the whole compound series of gneiss 

 should be connected with the same cause. 



Hitherto, I know not that any decided fragments 

 have been found in gneiss; although the occasional 

 occurrence of nodules of hornblende and quartz, round 

 which the laminae of the gneiss are incurvated, may 

 perhaps be supposed to bespeak a mechanical origin 

 for these. In Scotland, beds of a fractured and conglo- 

 merated gneiss are sometimes found adhering to the sur- 

 face of the ordinary rock ; a circumstance which has 

 been considered remarkable by Von Buch and other ge- 

 ologists; without reason, since it is a fact of no pecu- 

 liar interest. It is evidently the lowest portion of the 

 red sandstone series; as rioted under that head. 



The great features of gneiss, as they affect the pe- 

 culiar form and outline of a country, offer almost 

 every possible variety. In the Uists, Tifey, and Beri- 

 becula, and far more conspicuously in Sweden, it often 

 presents a dead level extending over a surface of many 

 square miles; in some places, without a single pro- 

 tuberance from which the subjacent rock could be 

 conjectured; while in the same islands, and elsewhere, 

 the surface becomes slightly undulated, with naked 

 protuberant masses, which, increasing in numbers, 

 confer a very singular character on Ron a and Coll, 

 and on some parts of Sutherland. In these places, 



