Vol. 57.] THE ORIGW OF THE DTJNMAIL RAISE. 189 



12. On the Origin of the Dunmail Raise (Lake District). By 

 Richard Dixon OLDHAii, Esq., E.G.S. (Read February 6th, 

 1901.) 



Etery visitor to the English Lakes, who has travelled by coach 

 from Windermere to Keswick, must know the Dunmail Raise, that 

 deep-cut wind-gap through the mountains which forms, if properly 

 understood, one of the most remarkable natural features that it has 

 been my^ lot to see, one of the most difficult of satisfactory expla- 

 nation, and one which has not by any means attracted the attention 

 that it deserves. 



Cut down to a height of 782 feet above sea-level, the gap lies 

 between the masses of Helvellyn (3118 feet) on the one hand, and 

 High Raise (1500 feet) and the Sea Fell Pikes (3210 feet) on the 

 other; it forms a typical instance of the liickenpass of Richt- 

 hofen,^ or wind-gap of the Americans, but differs from the 

 majority of such in one important point which will be brought out 

 in the sequel. 



Approaching the pass from the north, there is seen a deep-cut 

 valley, broad and open at the bottom, from which the sides rise 

 steeply in, what Mr. Marr has named, the curve of erosion; 

 it is, in fact, a typical stream-valley, and a valley properly belonging 

 to a volume of water to which the term river is applicable ; yet 

 when this gradual ascent is traversed the road, after a short steep 

 rise over a moraine, crosses an insignificant little streamlet, the 

 Birkside Gill, which is utterly out of proportion to the valley down 

 which it now flows, and is a very glaring instance of what Prof. 

 AY. M. Davis has called a misfit. As the road goes on, it traverses 

 the same valley-shaped gap, which ordinarily contains no stream at 

 all, till, at the summit, the Raise Beck is seen coming down from 

 the east. Here is a case of divided drainage, for while the bulk of 

 the water flows away to the south, a small portion, when the 

 beck is in flood, finds its way to the valley which has just been 

 traversed. 



So far nothing extraordinary has been seen, the features are such 

 as may be observed in any wind-gap due to the beheading of the 

 stream which once filled it, but as soon as the descent is com- 

 menced a great contrast is noticed. Instead of a steep descent on 

 the further side of the crest, the slope of the valley is at first 

 almost imperceptible. Then come some large moraines, signs of 

 erosion are seen in the stream-bed, there is a steep bit of descent 

 in the road, but the valley maintains the same type as on the other 

 side of the divide, and the Raise Beck is as glaring a case of misfit 

 to the valley that it occupies as the Birkside Gill. 



The commonest mode of origin of a wind-gap is when a stream 

 ' ' Fiihrer fiir Forschungsreisende ' 1886, p. 703. 



