340 ARRAN. ALLUVIA. 



of a mixture of clay, sand, gravel, and fragments of gra- 

 nite. These descend by degrees along the face of the 

 hill, and are deposited in the higher parts of the valley, 

 which is here the upper end of Glen Catcol. If these 

 materials are examined, they will be found to consist 

 solely of the granite of the hill itself, which is readily 

 distinguished among the other varieties the island affords, 

 by its small grained structure. As no streams descend 

 along this face of the hill, it is obvious that these alluvia 

 are the result of the gradual action of the ordinary atmo- 

 spheric causes on the bare rocks of the summit; their 

 gravity, aided perhaps by the gradual and constant drain- 

 age of the surface waters, urging them downwards till 

 they repose at length on the more gentle declivity of the 

 valley beneath, to be succeeded by fresh waste and fresh 

 deposits on the higher grounds above. The alluvia of 

 the valley are here therefore neither the result of the daily 

 action of torrents nor of remote diluvian causes ; and this 

 fact may be extended analogically to many of the High- 

 land valleys, where the real origin of those deposits is 

 rendered more doubtful from the similarity of the rocks 

 over large tracts of country, and where they have been 

 frequently attributed to the causes last mentioned. The 

 identity and the peculiarity of the materials, are here 

 sufficient indications of their true origin ; and the fact 

 itself is of importance in examining the nature of alluvial 

 deposits for the purpose of inquiring into the nature and 

 causes of those very obscure phenomena which seem 

 to record the former action of large bodies of water on 

 the earth's surface. 



The last alluvial substances worthy of being remarked 

 in Arran, are the blocks of granite which are found almost 

 every where dispersed over the island. These are of 

 various sizes, and often of an enormous bulk. Among 

 the great numbers which exist, I observed none bearing 

 the .marks of a distant origin; all of them, wherever 

 found, having the characters of the granites of the adjoin- 



