52 CHANNELS AND GLENS OF AYRSHIRE. 



a short distance further up on the right. Before entering the 

 recent rocky gorges, the glens or valleys have, as a rule, gently 

 sloping rocky sides, as is seen where they have been bared of 

 drift. In the gorges, the rocky sides, as already remarked, are 

 often wall-like and perpendicular. 



It is easy to see how the streams and rivers have left their old 

 drift-filled glens and formed new rocky ones. 



Vi __ 



B 



&■'?•/, 7%eore6i.cal Sec}* <»*.ofole(?rutv-j{t>tr Channels 



Let us suppose ABC (Figure i) to represent the section of an 

 old glen, which during the drift period was filled up with marine 

 deposits to the height of the line A C, perhaps a hundred feet 

 above the line of the old channel at B. On the re-emergence of 

 the land the stream may have commenced to cut a new channel 

 at any part on the line A C. If it commenced close to A, it 

 would cut out the rocky gorge ADE; and this is just what we 

 find the Ayrshire streams have often done. Should it have begun 

 near the middle of the line A C (which in the majority of cases 

 it has done), we will have a glen (or part of one) in drift with a 

 moderately sloping side and a steep side, as represented by the 

 dotted lines above B ; and, as drift is more easily excavated than 

 rock by a river, this glen may be a quarter of a mile or more wide. 



No one can say for certain (unless where both sides of an old 

 rock-glen have been laid bare) that any Ayrshire stream has 

 done much rock-cutting in the bottoms of the old glens. My 

 impression, after a good deal of examination of stream courses, is 

 that the bottoms of the old glens remain mostly covered with drift, 

 these channels having perhaps been the beds of sub-glacial rivers; 

 but few Ayrshire streams appear to run, in many places, exactly 

 in the lowest part of the old glens. That there are a number of 

 rock-bound hollows in Ayrshire, — like the area in which Loch 

 Doon lies, — partly or entirely scooped out by glacier ice, is quite 

 possible ; but the rocky gorges I am about to describe have not 

 been cut through barriers to such hollows, the only rocky barrier 



