336 ARRAN. ALLUVIA. 



open Talley, forming by far the most considerable extent 

 of flat land in the island, accompanies the courses of the 

 Blackwater and the Machrie. Nearly the whole of this 

 tract is alluvial, consisting of sand, clay, and gravel ; 

 and although hitherto almost neglected, it will probably 

 in no long time, and in the gradual progress of improve- 

 ment, form the principal agricultural district of Arran. 

 So great is the extent of this valley and so few the waters 

 which have their courses through it, that the origin of 

 its alluvial materials can scarcely be assigned to their 

 action. It is more probable that, like the former, these 

 have been the result of diluvian causes. 



The course of the Sliddery through a deep and very 

 narrow glen, is also marked by alluvial terraces. But 

 the origin of these, appears to be in the gradual destruction 

 and descent of the surfaces of the hills which bound that 

 glen and are composed chiefly of a tender red sandstone. 

 As far as I could discover the nature of these terraces 

 by examining those which were broken, they seemed com- 

 posed of the materials immediately at hand, bearing no 

 great marks of violence, or of distant transportation. It 

 is unnecessary to notice the deposits of minor extent 

 which accompany the smaller streams, since they all 

 concur in pointing out the same cause, namely, the hourly 

 action of running water on the surface. They are amply 

 illustrated by the banks which skirt the rivers descend- 

 ing from Glen Rossie and Glen Cloy, and of which the 

 ulterior transportation has formed the plain of Brodick 

 already described. 



Other alluvia, less easy to explain, are to be found 

 occupying the summits of low hills and extending over 

 considerable tracts. The most remarkable of these reaches 

 from Corryravie to the Bennan head; forming a range 

 of hills, of which the bases and more solid parts are 

 the sandstone strata that will be described hereafter. 

 The alluvial matter here, consists indeed of little else than 

 the sandstone and the red clay which would result from 



