w. 



Tol. 68.] GLACIATION OE THE BLACK COMBE DISTRICT. 429 



to denudation. Beds of sand and gravel also occur on the south 

 side of Grassoms Beck, a few hundred yards east-south-east of 

 Gibson's Spout ; and on Bootle Bank they form a rather flat-topped 

 feature, rising from a platform of andesite to 400 feet at its highest 

 point (fig. 10, p. 432). 



A pit at the northern end of the feature gave the following 



section : — 



Thickness in feet. 



Layers of stratified sand and gravel, with boulders measuring 

 up to 18 inches in greatest diameter 15 



Well-stratified red [Triassie] sand and finer layers of gravel, 

 chiefly of granite, lava, ash, etc. with occasional boulders. 4 



The pits on Bootle Bank also contained fragments of red 

 sandstone and striated slate. 



These gravels are comparable with those describe^ above as 

 having been formed on the granite tract, but they differ in their 

 more regular stratification and by lying at a higher general level. 



Fig. 7. — Profile section of the parallel sequence of marginal channels 

 in the volcanic rocks near Bootle. 



Bramirc Nettle Crag:s Damkiik Moraines 



Xength of section = 1 mile. 



They were probably accumulated beneath the waters of an ice- 

 dammed lake about half a square mile in extent, held up in the 

 embayment north of the north-western shoulder of Black Combe. 

 The water drained away through, or over the ice, leaving no trace 

 of its exit. 



At a later stage, about the time when the Kinmont Channel 

 was first initiated, and when a small lake probably existed at its 

 lower end, these gravels began to be degraded and removed by a 

 definite stream which finally cut the Damkirk Channel through the 

 underlying andesite. 



The andesitic ridge would form a more formidable barrier than 

 the granite, for the rock decomposes less easily, and would not 

 have been so thoroughly rotted to begin with. Consequently the 

 drainage-channels are narrow and steep-sided, and begin and 

 terminate rather abruptly, for the drift banked against the ridge 

 has been to some extent removed by post-Glacial erosion. 



As the water-level fell, roughly stratified or false-bedded gravels 

 were formed at successively lower levels near the heads of the 

 drainage-channels. A section 8 feet or more in depth, at the head 

 of the Bramire Channel, shows sand and gravel with boulders up to 

 2 feet in greatest diameter, on coarse sand and gravel, resting upon 

 fine sand and gravel inclined in a south-south-easterly direction, 



E. 



