ON THE GLACTATION OF EAST LOTHIAN SOUTH OF THE GARLETON HILLS. 23 



in a westerly direction. The phenomena are well marked and quite unmistakable. To 

 understand this interesting complication one must recognise that the system of channels 

 lies wholly above the 900-feet contour ; that is, above the summit level (884 feet) of the 

 Heriot railway pass, six miles to the west. An examination of this pass shows that it 

 was actually employed as a glacial drainage channel by waters travelling from north to 

 south across the hills. As a matter of fact the pass was sometimes used in the reverse 

 direction also, but when available for the northern drainage, it of course offered an 

 opportunity of escape for waters empounded in front of the retreating ice sheet for some 

 distance to the east of its entrance as well as to the west. 



Now a glance at the general map will show the even course followed by the 1000- 

 feet and 900-feet contours between the mouth of the Heriot Pass and the northern 

 slopes of Lammer Law, and it will be readily understood that very slight differential 

 movements of the ice front might lead to flow of water in the one direction or the other 

 across the ridge we are at present considering. 



N.W. 









CENTRAL 



VALLEY GLACIER 



























cohiE burnCLA_ 



at*. 



SCALL Of MILES 



M/ir/CAL SCALE 

 THREE TIMES HORIZONTAL 



Fig. 4a. 



Having discussed this point, the next question is as to whether the channel ABC, 

 draining east, was cut earlier or later than the channel BD which drains west by various 

 mouths. The answer is attained by a line of argument already developed in a previous 

 section. The top of the channel cut at A is higher than any point in the bottom of the 

 channel B D draining west from B, therefore it would seem that A was cut before B D. 

 The water entering # at the intake A flowed across the low col in the water shed at B, 

 and then, instead of following the uniform slope of the hillside down into the Cowie 

 Burn, was deflected so as to run along the side of the ridge, cutting a channel B C, forty 

 feet deep, in this position. One can scarcely avoid the conclusion that this channel 

 started in a gutter of which the south-eastern wall was the front of a small glacier 

 occupying the Cowie Burn valley. Once, of course, the stream had lowered its bed into 

 the rock of the hill side it would become self-supporting and could dispense with aid 

 from the local glacier. All the time, however, the great ice sheet must have remained 

 to impound the lake that discharged through A. We are justified, then, in picturing a 

 time when these two glaciers, the large and the small, faced one another across the 



* This is the condition of affairs shown in fig. 4, although the other channels of the district are also shown. 



