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



the difference between the two does not amount to more than four feet, showing clearly 

 that the post-glacial vertical erosion has, in this case, been quite trivial. Standing below 

 the junction of the two confluent valleys we obtain a good view up both, and are able 

 to appreciate at once their similarities and their contrasts. They are both gorges 

 bounded by steep walls ; but while the deserted channel has lost some of its original 

 abruptness of outline, owing to the collection of rain wash, it evidently retains a feature 

 which in the case of its neighbour has been more or less completely obscured by the 

 action of the stream. For at every convexity in the course of the dry valley the outer 

 ■wall is more steeply cut than the inner, showing that the valley was excavated by a 

 stream accurately proportioned to the channel it was cutting for itself,* and of quite a 

 different order of magnitude to the Spott Burn. 



The role played by the Spott Burn during post-glacial times may now be readily 

 appreciated. Since ever its volume has become so greatly reduced it has wound in 

 small meanders along the valley bottom, cutting now into the one side, now into the 

 other. In this manner it continually supplies itself with as much material as it can 

 transport, and thus as the meanders work gradually down stream, the valley is widened 

 but nowhere materially deepened. 



Two or three equally striking examples occur in the neighbourhood of Garvald, but 

 it is important now to point out that some of the East Lothian streams left in occupancy 

 of glacial drainage channels have proved themselves capable of accomplishing a notable 

 amount of vertical erosion, and to recognise that in such cases the resultant changes can 

 readily be distinguished. The Braidwood Burn,t a little south of Innerwick, is an 

 excellent case in point. It is a powerful stream, and has cut for itself a pronounced 

 gorge, but the result is far more accurately described as a dissection of the floor of the 

 old valley, rather than a deepening of the same. For the work of the recent stream, 

 with its greatly diminished volume, has been to cut a gorge that winds to and fro along 

 the old bottom, the latter being in large measure still preserved intact. 



It is worth while before leaving the subject of these channels to take note of the 

 enormous volume of water which they must at times have been called upon to conduct 

 away. They served to carry off the drainage, not only of the Lammermuirs, but also of 

 the Moorfoots, and in fact of the whole of the Mid Lothian basin, except in so far as 

 leakage was permitted here and there through the fissured margin of the ice sheet. 

 During the earlier stages of retreat this western drainage sometimes found a short cut 

 across the watershed by the pass between the Moorfoots and Lammermuirs, which has 

 been taken advantage of in our own days for the railway leading south to Galashiels. 

 But the summit level here is 884 feet, so that for a long period this short cut was not 

 available, and the Mid Lothian drainage had perforce to pass right across East Lothian 

 and part of Berwickshire to reach the sea. Several routes were successively employed 



* This is a genera] feature of dry valleys. See Glacier Lakes in the Cleveland Hills, p. 483. The type example 

 for East Lothian is furnished hy the Danskine Loch channel, two miles east of Gifford. 

 t PI. II. fh.'. 2. 



