216 REMARKS ON THE GNEISS ISLANDS. 



CONCLUDING REMARKS ON THE GNEISS ISLANDS, 



ALTHOUGH the tracts thus described comprise the 

 chief masses of gneiss which occur in the Western 

 Isles they do not include the whole, as will appear in 

 the account of those islands which are to follow. The 

 complicated structure of these rendered it proper to 

 arrange them in a separate division. But in consider- 

 ing those portions which consist of gneiss, there 

 appear no circumstances requiring such notice as to 

 render it necessary to defer this general comparison. 



From the dispersed nature of the preceding remarks 

 on this rock it will be useful to bring the whole of its 

 leading characters into one general view : a proceeding 

 the more necessary as they appear never to have been 

 clearly defined. It is not however in this view pretended 

 to give a complete history of gneiss, since the remarks 

 are only deduced from investigations limited to Scotland. 

 They will still serve as contributions towards a more 

 perfect one at some future period. 



The great, or picturesque features of gneiss present every 

 possible variety. It often exhibits a dead level for a consi- 

 derable space ; as in Tirey, Benbecula, and other islands 

 above described ; the only access obtained to the naked 

 rock being from some pool of water or accidental breach of 

 the surface. Occasionally, as in Lewis, protuberant masses 

 are seen breaking through the soil. These become 

 in other situations, as in Coll and Rona, so numerous, 

 that, on a general view, nothing but a continuous extent 

 of rock can be seen ; the small quantity of herbage, with 

 the occasional lakes that occupy the intermediate spaces, 

 being only visible in the immediate vicinity of the spec- 

 tator. These rocky bills nirrly exceed an hundred 



