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



operations in the neighbourhood of Ormiston, of which Dr Crampton has kindly given 

 us the following interesting account. " To the west of Ormiston, the light railway 

 follows what has at one time been an important line of drainage. It is shown by bores 

 to be in large measure choked by alternating deposits of sands and gravels, and it is 

 occasionally so completely filled up that its edges no longer make a feature at the 

 surface. Another channel lying to the south and east of Ormiston, and passing close by 

 Pencaitland, has also been proved to contain a considerable depth of clay and sand, and 

 from some of the bore records it can be definitely recognised that boulder clay here 

 occurs superimposed upon sand and mud. The journal of one of these reads as 

 follows : — 



Surface, 1 foot. 



Clay and stones, 17 feet. 



Sand and gravel, 13 feet 10 inches. 



The hollow, despite its partial infilling, is still strongly marked and appears to have 

 been reopened to some extent by the flow of water at the time of the retreat of the ice 

 sheet which had deposited the boulder clay mentioned above. The explanation which 

 seems most applicable to these two channels is that they were marginal stream courses 

 formed in front of the ice sheet during its oscillatory retreat, and therefore liable at 

 times to be overwhelmed by a temporary re-advance of the glacier and in this manner 

 choked with boulder clay." 



III. The Upper Limit of Marginal Phenomena set by Local Glaciation. 



We have, up to the present, been dealing with the phenomena which marked the 

 retreat of the great ice sheet from about the 1000-foot level downwards. Above this 

 the processes at work were evidently somewhat different, for they have left a record of 

 their operations which, though meagre, is still eloquent of the special conditions 

 prevailing during the earlier phases of the retreat. As soon as the Lowland ice had no 

 longer power to surmount the Lammermuirs, the dissected plateau in which this range 

 culminates became for the time being an independent area of dispersal, though still 

 retained within the confines of the great ice sheet. Even when the latter had shrunk 

 back for some little distance from the summits of the hills, every hollow and valley was 

 choked with neVe\ and many a one nourished its own little glacier, so that every here 

 and there a tongue of ice still reached down the gentler slopes to join its great 

 companion in the lower ground.* So long as this last condition held, it is obvious that 

 marginal drainage on a large scale must have been impossible, and we have at once the 

 explanation of the upper limit referred to above. Later, however, a stage arrived when 

 the Lowland ice parted company with the local glaciers, for while the former continued 



* It must not be overlooked that the evidence adduced in this and the preceding section has » most important and 

 direct bearing upon the climatic conditions of the period. 



