VII. 



THE BURIED, OR DRIFT-FILLED 

 CHANNELS AND GLENS: 



AND THE 



POST-GLACIAL GLENS OF AYRSHIRE. 



By John Smith. 



With a Map and Five Diagrams by the Author. 



(Paper read 5th May, i8qj.) 



During my examination of the Ayrshire drift formation, in going 

 up or down the various stream courses I was constantly passing 

 from parts of the valleys where banks or scaurs of drift, sometimes 

 reaching to as much as 100 feet in vertical height, occurred, into 

 other parts where there was little or no drift at all, but where the 

 streams had cut deep narrow gorges through rock, with more or 

 less perpendicular walls. These features, presenting themselves 

 so often, led me to take special notes, and I soon found that the 

 rocky gullies were clearly post-glacial, and that to one or other side 

 of them there was a pre-drift glen. I say pre-drift advisedly, as 

 there are possibly no pre-glacial glens in Ayrshire, correctly 

 speaking, all of them, apparently, having been increased in size 

 during the early part of the glacial period by glaciers, the pre- 

 drift glens being filled up with boulder clays and intercalcated 

 beds of sand, gravel and laminated clay ; sometimes these latter 

 beds lying on the rock, and the sands and gravels occasionally 

 capping all, but oftener this position is occupied by boulder clay. 

 After a little practice it became quite an easy matter, generally 

 speaking, to tell to which side of the streams the filled-up glens 

 lay. If, for instance, on going up a stream, rock would appear on 

 the right-hand side, the drift continuing for some distance on the 

 left, then the drift would disappear, and finally the river was rock- 

 bound on both sides ; the filled-up valley in this case would be 

 on the left side ; and in getting out of the rocky gorge the drift 

 would again appear, first on the left side, the rock continuing for 



