April, 1895. FORMS OF MOUNTAINS. 241 



those of temperate regions, and accordingly for most of the mountain- 

 forms of the globe ; but under exceptional circumstances, and on a 

 small scale, we find mountain-slopes existing in ordinary temperate 

 regions which have been produced in the dry way. In arctic and 

 high alpine regions the prevalent sculpturing agent is frost ; in deserts, 

 changes in the temperature of the atmosphere working directly, or 

 indirectly through the medium of winds ; in temperate regions, rain 

 and rivers. 



The familiar forms of mountains in temperate regions are fully 

 accounted for by G. K. Gilbert in his work on " The Geology of the 

 Henry Mountains " ; it is there shown that stream-denudation tends 

 to produce curves which become steeper and steeper as one ascends 

 from sea-level towards the highest part of a country, so that if a 

 country were elevated by a symmetrical uplift, which would give the 

 land a convex curve, that curve would be gradually replaced by two 

 concave curves of stream-erosion, having the form indicated above, 

 and meeting at the main watershed. These curves of stream-erosion 

 are the curves which bound hills and mountains in temperate regions, 

 after stream-denudation has been in operation for a sufficiently lengthy 

 period. They may be seen to perfection in any hilly district in 

 Britain. It would be difficult to find a better example than the 

 rocky peak of Bowfell, on the outer edge of the Scawfell group. From 

 every side the two curves may be discerned, though they are best 

 seen when looking southwards from the Borrowdale valley, or north- 

 wards from Eskdale. Great Gable, as seen from the foot of Wast- 

 water, also exhibits these curves, and they are repeated below in the 

 slopes of the nearer fells. In Mrs. Lynn Linton's book on the Lake 

 Country, the engravings of W. J. Linton draw forcible attention to 

 them ; special mention may be made of the view from the top of 

 Helvellyn looking over Striding Edge (facing p. 149), and the beautiful 

 outline of Gimmer Crag on the Langdale Pikes (p. 170) " as it rises 

 in one unbroken up-springing line from the dale to its height of over 

 2,000 ft." But it is needless to cite further examples : the curve of 

 stream-erosion is the dominant curve among the hills of our island. 



The details of form of hills carved by stream-erosion depend to 

 a large extent on the alternation of soft and hard rocks, and the 

 inclination of the planes of stratification ; but in hills carved out of 

 homogeneous rock, the character of their outlines is independent of the 

 nature of the rock, though the slopes of the curves of stream-erosion 

 vary. As an illustration of this, the remarkable hills standing west 

 of the great escarpment of the Pennine Chain in Cumberland may be 

 mentioned. Two of these, Dufton Pike and Murton Pike, show the 

 curves of erosion fairly well, though in both cases they are somewhat 

 masked owing to the existence of soil on the hill-slopes : these hills 

 are quite similar in outline, though Murton Pike is formed of soft 

 clay-slate, and Dufton Pike of hard rhyolite. The similarity of pro- 

 portion and outline is determined by the trend of the bounding valleys, 



