EDEN VALLEY AND YORE!SHIRE-DALE DISTRICT. 73 



the sweeping curves and generally unencumbered lower slopes 

 that are usually seen about the lower terraces. Some of the scars 

 are more than 1000 feet above the bottom of the adjoining valley ; 

 and as no stream could possibly now along the slopes in such a way 

 as to carry off the talus from the scar, unless the valley were shal- 

 lower by several hundred feet than it is at present, river-action 

 cannot be taken into account, unless it can be shown that in the 

 north of England, with a high rainfall, a river can cut its channel 

 down more than 1000 feet while the scars above only recede a few 

 feet from the line at which they were first formed. Many of these 

 scars, too, can be shown to follow the undulations of the beds, so 

 that the top of the scar at one place is often much lower than the 

 base at another a few hundred yards off. 



Ordinary weathering in nearly every case is tending to cut back 

 some of the most precipitous scars into rounded slopes. Where 

 the scar is of limestone it is often banked up by a talus of small 

 weathered chips detached along the joints and bedding -planes from 

 the higher part of the scar ; and it is obvious that, unless a stream is 

 at work below carrying off the weathered material, the talus will 

 accumulate, protecting the lower part, while the top of the scar 

 weathers back into a low slope, the result being a small escarpment 

 quite unlike the bold lines of scar seen in the dales. 



Professor Hughes pointed out to the writer in 1868 that the sub- 

 aerial agents just referred to were inadequate to produce much of 

 the present form of the ground in the dales, and that land ice must 

 have had a large share in bringing the rocks into their present 

 shape. 



When we know that in the upper parts of Wensleydale and 

 Swaledale, and in some of the adjoining valleys, the ice must have 

 been at the least 1600 feet in thickness, the facts mentioned above 

 become intelligible. It is easy enough to understand how such a 

 mass of ice — charged throughout with stones of all sizes, and flow- 

 ing between fells which are made up of alternations of hard and 

 soft beds lying nearly horizontally — would cut with most ease into 

 the soft beds, so as to leave much of the less easily eroded rocks 

 standing out as terraces and scars. This explains how it is that 

 the swallow-holes are confined to the inner margin of each terrace, 

 and that the terrace is nearly uniformly weathered all over. All 

 the preglacial terrace, swallow-holes, joints and all, was carried 

 away by the ice j and when this disappeared a new surface of rock 

 was left for the weather and streams to act upon. 



The next hill-slope above the terrace has been cut back so little 

 in Postglacial times that it is often not more than a few feet from 

 the centre of the swallow-hole — that is to say, from the position in 

 which it was left at the close of the Glacial period. 



Glacial markings are occasionally met with on these terraces close 

 up to the inner margin, affording another proof that they are nearly 

 as the great ice-sheet left them. 



This theory helps us to understand how it is that on some of the 

 hill-slopes terrace above terrace exhibit so remarkable a conformity 



