64 COLONSAY 



action. In glacial times, so we are told, the whole of the 

 country, like the north of Greenland at the present time, 

 was overflowed with ice, which ground and smoothed all 

 the rough surfaces. But the softer rocks, readily affected 

 by the weather, have in the lapse of intervening ages lost 

 much of the rounded outline acquired during the glacial 

 period. Nevertheless, a careful examination will discover 

 well - smoothed and well - striated surfaces. These striae, 

 which are very well seen on the rocks rising from the 

 strand, were caused by the rubbing of stones as they were 

 pushed along the surface by moving glaciers. They agree 

 in the general direction in which they run east to west 

 and this shows that the ice, as might be expected, flowed 

 from the mainland. Here and there, in hollows and on 

 the hill-sides, boulders carried by the ice, differing in 

 structure from the surrounding rocks, are met with. 

 Messrs Wright and Bailey have identified boulders of 

 granite from Glen Fyne, porphyries from Loch Fyne, 

 pebbly sandstones and red conglomerates from an unknown 

 source ; also schists, such as those of Jura and Crinan, and 

 other kinds of rocks not entering into the formation of 

 Colonsay. These " erratics," which were carried along by 

 the ice, point to a prolonged movement from the easterly 

 direction. 



Boulder clay or till is met with in hollows in various 

 localities. It is usually a reddish coloured, gritty clay, quite 

 unstratified, and abundantly charged with angular and sub- 

 angular stones and boulders, not a few of which show 

 finely striated surfaces. Many of the stones are of local 

 origin, while others come from a distance. The distribution 

 of the boulder clay confirms the supposition regarding the 

 direction from which the ice came. It is generally found 

 in situations sheltered from the full brunt of the ice as it 

 flowed from the mainland. Ant-Allt-ruadh (the Red Burn) 

 has probably derived its name from the discoloi'ation of its 



