28 Hugh Miller — Escarpments and Terraces. 



one line of strike for the next two miles, but we need follow it no 

 further. 



Before quitting this portion of the subject, I may adduce one 

 other proof of the j)re-glacial origin of gaps — derived from the 

 Whinsill. This basaltic dyke is interrupted by numerous narrow 

 steep-sided breaks not usually stream-traversed. The edges of these — 

 especially, I think, those opposing the glacier— bear the characteristic 

 roclies moutonneed aspect ; while the interiors, lying out of the reach 

 of a planing agent, are untouched. The bearing of this fact upon the 

 present question cannot be mistaken. 



2. Belations of the Escarpments to Glacial Erosion. — The escarp- 

 ments, as already stated, are by no means of equal development 

 along their line of strike. Sometimes, when favoured by the con- 

 stitution of the rock, they stand boldly out ; but anon the bedding or 

 texture alters, and they lower and subside — often being temporarily 

 lost altogether. Even the best-marked escarpment is thus separated 

 up into segmented portions, which, in general, present in front 

 view an arched outline — a rounded middle development sloping or 

 curving down east and west. Bearing in mind that the glacier 

 passed eastward nearly along the axis of each escarpment, it will be 

 remarked that we have here the conditions most favourable to the 

 formation of moutonneed outlines ; — of a long, smooth, sorely abraded 

 side facing the glacier, and a steeper sheltered one averted from it. 

 It is a fact, nevertheless, of strikingly constant recurrence, that the 

 segments described turn their steeper slopes westward, the acclivities 

 opposed to the glacier often being so abrupt as to remind one of 

 sloped gables. This fact, apparently unconnected with any peculiarity 

 of internal rock-structure, I believe to be explicable by the prevailing 

 westerly winds causing excessive weathering and more rapid reces- 

 sion on that side ; for, as the dorsum of each segment is the most 

 massive and durable portion of the bed, the frequent beat of the rain 

 swept eastwards must eat further in towards the solid core of 

 rock, the slope thus weathered partaking more of the abruptness of 

 the escarpment's middle face. How exposed that western side is to 

 the battering of the elements, many old buildings amply testify. 

 The eastern side may be comparatively smooth and even, each block 

 rectangular, and some tool-marked, and the mortar nearly continuous 

 between surfaces; while the western side is deeply weather-scarred — 

 the stones projecting in rounded bosses, and bounded by crevices, 

 whence mortar has been removed. The material disintegrated from 

 the stones of the westward face of the old peel-tower of Chipchase 

 Castle (date about 1280) must amount to several ounces apiece, 

 while decay has scarcely touched the sheltered sides. To the same 

 cause the feature above described may probably be imputed, but in 

 any case it gives no countenance to the theory of the glacial origin 

 of escarpments. 



Assuming, however, that such was their origin, that each escarp- 

 ment was progressively developed by the removal by ice of a softer 

 bed covering it, the portion of the dip-slope latest bared would 

 necessarily be saved vast erosion, of which the brow bore the full 



