CXviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I906, 



shown in section, as the result of mere coincidence. Leaving out of 

 consideration for the moment the supposed capture of Wastdale, we 

 have in order, the mouthing of the Sty-Head Tarn Beck above 

 Taylor Gill, that of Gillercombe and that of the Honister Yalley, 

 and the cols west of High Doat and Castle Crag respectively. 



The depressions in which these cols occur certainly suggest parts 

 of an old valley, and especially is that the case with the depres- 

 sion behind Castle Crag, which (when viewed from High Doat) 

 presents a U-shaped cross-section like that of a fairly-important 

 river-valley. 



Granting the deepening of the present Borrowdale valley between 

 the mouth of Combe Gill and the Jaws of Borrowdale (which must 

 have taken place, though not necessarily in the way discussed above), 

 the explanation of these features is simple. Beginning downstream 

 we first notice that the main Borrowdale stream has shifted west- 

 ward, west of Rosthwaite, where a great sweep of alluvium runs, to 

 the concave fell-side, where Tongue Gill comes down. This westerly 

 shifting of the stream would gradually cut away the ridge between 

 Borrowdale and the upland valley, diverting its waters into Borrow- 

 dale, and leaving the part of the upland valley on the north as the 

 depression west of Castle Crag. 



But the most important change would be the similar action of 

 the Combe-Gill stream on the west at the foot of Honister. The 

 evidence points to the present and old valleys having formed two 

 loops at this point with their convexities approaching one another. 

 If the Combe-Gill stream cut into the upland valley, the upper 

 waters of this would now be diverted into the main Borrowdale 

 valley (this may have happened before or after the capture west of 

 Rosthwaite). 



Thus the High-Doat depression would be converted, like that of 

 Castle Crag, into a wind-gap. But the most important result would 

 be that the stream, which formerly flowed from off the Seathwaite 

 shatter-belt to a part of the valley (between Honister and Castle 

 Crag) not occupied by such a belt, would be put in connexion 

 with the Borrowdale stream, which had already deepened its course 

 along its belt ; and therefore the Seathwaite stream would now be 

 capable of deepening its valley. This it has done to the head of 

 Grainsgill, leaving Honister, Gillercombe, and the Sty-Head valley 

 as hanging valleys. 



We now pass to the consideration of the head of the Sty-Head 



