THE 



GEOLOGICAL MAGAZINE. 



No. LXXVI.— OCTOBER, 1870. 



I. — On the Origin of the Drifts, so-called Moraines, and 

 Glaciated Eock-Surfaces of the Lake Distriot.'^ 



By D. Mackintosh, F.G.S. 



(PLATES XXIV. and XXV.) 



THE Lake District differs from other parts of England in the 

 comparative absence of table-lands or broad upland plateaux. 

 The original mountain-masses have in most parts been eaten into by- 

 denudation to such a depth as to leave only a series of narrow 

 ridges or edges which act as buttresses to small peaks. When the 

 pedestrian has climbed up from the inner end of one profound ex- 

 cavation, he finds himself on the brink of another. The larger 

 valleys are deeiDCst at their inner ends, and shallow out and narrow 

 off towards their entrances. Their floors fall so slightly outwards 

 that were the outlet stream-channels to be filled up, the valleys 

 would be converted into troughs. In most instances their mouths 

 are confronted by higher ground, and this is sometimes so strikingly 

 the case that in approaching a valley from the surrounding belt of 

 Carboniferous strata, you find yourself going down instead of up 

 among the mountains. The highest ground is not in the centre, but 

 irregularly surrounds a comparatively depressed area about ten 

 miles in average diameter. Such a configuration of country could 

 not have been the best adapted for accommodating a quantity of 

 snow at a high level sufficient to send very large " tongues of ice " 

 along the radiating valleys. During the glacial period the whole 

 district was probably enveloped in an ice-sheet, which may have 

 glaciated rock-surfaces, and, by its grinding action, worked up a 

 great part of the matter now composing the Boulder-clay ; but the 

 surface-configuration of the district renders it difficult to conceive 

 how, during the gradual increase or diminution of the ice-sheet, 

 very extensive glaciers, separated by ridges not buried under ice, 

 could have been supported in at least many of the valleys. In. 

 favourable positions, however, valley-glaciers may for a time have 

 existed, and may have smoothed and striated rock-surfaces. They 

 may likewise, especially in the more abrupt-sided valleys, have 



1 In the article on Shapfell Boulders (Aug., 1870, Vol. VII.), p. 350, line 9 from 

 foot of page, for Stainmore, read Stainmoor ; same page, line 13 from foot, the I in 

 Kendal was omitted. 



VOL. VIT. — NO. LXXVI, 29 



