54 GEOLOGY OF ARRAN. 



upper portions of the formation. The lower portions are seen 

 farther up the glen, but at some height on either side, in the 

 wood and moor on the left, and the hill-side on the right. They 

 are very coarsely conglomerate. Specimens of both varieties 

 may be seen in the stone fence by the side of the wood. 



rf 



Fig. 14. 



(a a) Sandstone and conglomerate ; (b) productus limestone ; 

 (c) old red sandstone ; (d) schist ; (e) granite. 



The alluvial mound at the entrance of the glen has been 

 noticed already, as most probably the terminal moraine of a 

 glacier which once filled the valley. It is precisely in the 

 position where such a moraine would have been thrown 

 down, and consists of such materials as the ice would have 

 borne forward ; and its height places it far above any existing 

 river action. It appears to have extended, at some former 

 period, entirely across the opening of the valley, backing against 

 the hill side on the south, as it now does in the opposite direc- 

 tion, and forming the barrier which confined a lake, occupying 

 at that period the lower portion of the glen. The bursting 

 of such barriers, and their subsequent modification by floods 

 in the river, are common phenomena in mountainous districts. 

 Traces of a lateral moraine are seen on both sides; and 

 farther up the glen, where it turns northwards, two other 

 mounds, rising high above the stream, are in the position 

 where a terminal moraine would be thrown down, after the 

 ice had retreated from the lower part of the valley. 



The discovery of an anchor in Glen Rosa, similar to those 

 now used by the herring smacks which visit Brodick Bay, 

 has often been referred to as proving that since the island 

 was inhabited by a people far advanced in civilization, the 

 sea filled the valley, and afforded a " trustworthy station for 

 ships." That an anchor was really found, brought to the 



