80 BAURA. SOIL, ALLUVIA. 



times found forming very thin beds under the peat, which 

 is however in general much too deep to admit of this 

 matter being reached by the agricultural processes in use, 

 so as to be brought into action. 



As there are no beds of the usual alluvia of flat lands 

 in Barra, so there is none of the mountain alluvial matter 

 so common in hilly countries, which consists of mixtures 

 of angular stones with clay. The gneiss of these islands 

 appears indeed to be of a very refractory nature, under- 

 going little change from the action of the atmosphere. 

 The surfaces are smoothed as if from the very slow 

 effects of air and water, but in general the angles are 

 tolerably sharp, and the traces of fissures penetrate to 

 no depth. Every thing appears in its place ; the pre- 

 cipices which result from the fall of rocks are rare, few 

 fragments are scattered about, and those which are, 

 have an integrity and freshness rarely found in any 

 other class of rocks in Scotland. A spectator cannot 

 help being struck by the aspect of obstinate durability 

 which they display. If we compare this gneiss with 

 granite, with mica slate, with quartz rock, with lime- 

 stone, or with trap, its superior powers in resisting 

 destruction will be strikingly apparent; while the ima- 

 gination is lost in reflecting On the slowness of those 

 changes by which many parts of the rocky globe were 

 first made fit for the habitation of plants and animals. 



The difficulty with which this rock decomposes into 

 earth, is the evident cause of the nakedness of the 

 surface. If the lichens find a hold, it is true that they 

 are followed by their usual attendants, the mosses, the 

 rushes, and the grasses, which in the end produce a body 

 of green covering wherever they can effect a lodgment. 

 But this covering is only peat. The peat is laid on the 

 naked rock, and the vegetation of one generation of 

 Scirpi or Sphagnum is followed by that of others in 

 endless succession, without change or amelioration. The 

 cause of the extreme resistance of this gneiss is not 



