8 PROFESSOR P. F. KENDALL AND MR E. B. BAILEY 



had been collecting, and these re-advancing across the path of a glacial stream it drives 

 the occupant back again into some deserted channel further up the side of the hills. 



A point of special interest is the fact that all these effects are restricted below a 

 more or less clearly defined upper limit (see fig. 1). Marginal streams and temporary 

 lakes have scarcely left a trace of their former presence in the higher portions of the 

 hills. Yet it can be demonstrated that this does not mark the upper limit reached by 

 an invading ice sheet, but rather the level at which the retreating ice parted company 

 with its lineal descendants, the little glaciers of its high-level valleys. 



Moreover, the district has furnished fresh evidence regarding the relations which 

 locally prevailed between land, ice, and water, when the ice sheet had already withdrawn 

 into the low ground ; and, probably what will attract more general interest, it has 

 supplied a number of very beautiful instances of a special type of stream capture, which 

 has greatly influenced the plan of the glacial drainage system. Without entering into 

 detail at present, it is sufficient to say in this connection that there are many cases 

 where a tributary stream has thrown out a cone or delta into a deserted glacial drainage 

 channel and has thus succeeded in establishing a watershed within the latter.* 



In order to illustrate the various aspects of the subject alluded to above, we will 

 arrange the evidence under the following heads : — 



I. Phenomena illustrating the general conditions which attended the retreat of the 



great ice sheet. 

 II. Phenomena illustrating the oscillatory nature of the retreat. 

 III. The upper limit of these marginal phenomena set by the confluence of the 



local glaciers with the great ice sheet. 

 IV. The influence of corroms t and bridge-deltas in modifying the glacial drainage 



system. 

 V. Evidence regarding the level of the sea at the time of the retreat of the ice 

 sheet. 



I. Illustrations of the Phenomena Attending the Retreat 

 of the Great Ice Sheet. 



East Lothian illustrates extremely well two distinct though cognate aspects of the 

 phenomena which attended the retreat of the great ice sheet. One notices everywhere 

 records of the operation of water under special conditions of restraint ; in one place the 

 manifestation may take the form of some monumental piece of erosion, in another of 

 deposit, but everywhere the phenomena point to the action of water, and of water 

 impounded in front of the retreating ice sheet. One of the consequences of this 



* Dr Crampton independently arrived at precisely this interpretation in accounting for the partial reversal of 

 the drainage in the Borthwick dry valley, to which further reference will be made in the sequel. 



+ Corroin (cothrom) is a Gaelic word used in place names in the Ardgour district of Argyllshire, to denote a. 

 delta-watershed. Its literal meaning is a "balance," and it is intended to illustrate that a stream issuing upon such 

 a cone has the chance of flowing either the one way or the other. 



