32 " Hugh Miller — Escarpments and Terraces. 



more clearly do the mural planes stand forth. With regard to the 

 absence of severe weathering in front, alleged by Mr. Goodchild, 

 it is certainly wonderfully inconspicuous ; but I have shown that to 

 accept the glacial hypothesis is by no means to get rid of the diffi- 

 culty. Glacial erosion may well have been sufficient at least to 

 remove any raggedness of surface or edge that may have been, 

 leaving smoothly dressed surfaces for weathering to commence afresh 

 upon. 



When the strata are free from superficial deposits, the swallow- 

 holes observable in the Northumberland limestones resemble those 

 of Yorkshire, as described by Mr. Goodchild, in usually bordering 

 the foot of the dip-slope. They are circular pits of the shape of a 

 common filter, and although in most cases the circle is indented on 

 one side by the feeding runnel, they exhibit no great tendency to 

 lengthen out into trenches, even when copiously fed with peaty 

 water. The amount of limestone removed from, the external orifice 

 is usually very trifling, seldom exceeding a foot or two in diameter. 

 Indeed, judging from the dissolution eflected in these cases by water 

 acting under very favourable conditions, — namely, well charged with 

 carbonic acid and constantly renewed, — it might well be thought that 

 the liability of exposed limestone surfaces to dissolve has been over- 

 estimated. From the frequency with which new swallow-holes are 

 formed, I believe, however, that they either are temporary and liable 

 to be discarded and filled up, or that they are of very recent origin. 

 There is certainly no proof that any of them are pre-glacial, and 

 from their inconsiderable depth, seldom over ten feet, they could not 

 be expected to have weathered the Ice Period. It is impossible to 

 affirm, then, that in pre-glacial times they did not witness more 

 strongly to atmospheric denudation than they now do ; the vertical 

 fissures exposed in limestone quarries may well have given rise to 

 swallow-holes atop, which travelled back, in the manner required 

 by Mr. Goodchild, as the covering of shale was cut into. 



The relation of springs to the escarpments, although interesting, 

 I will not enter into. I am not aware that they are regarded as 

 other than interferences with the regularity and sharpness of scarped 

 outlines, still less as productive of symmetry such as frequently meets 

 the eye in Wensleydale. In Northumberland coomb-like features 

 are produced occasionally around their outburst, though of course in 

 miniature. 



Passing now to the features of local development of the Yorkshire 

 terraced escarpments cited as difficult of explanation, two of these 

 are probably stated as adverse only to the fluvial theory of the terrace- 

 formation, and may be dismissed with a word. That scars should be 

 in correspondence on opposite sides of a dale is due of course to the 

 regular extension of the beds across the intervening space now ex- 

 cavated. Where the duplicate faces happen to crop out, there will 

 the terrace rise into relief. The same reason applies to the persist- 

 ence of the scars in accompanying disturbed beds " through all their 

 variations of position and inclination." On the Glacial Erosion 

 hypothesis, such sloped outcrops would be related to a glacier moving 



