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Professor J. W. Gregory — 



When the glaciers flowed down the valleys they would have worn 

 back the spurs, levelled the bars of rock on the floors, and thus the 

 trough shape of the canyons, due originally to their formation along 

 rectilinear fractures, was rendered more complete. The amount of 

 solid rock removed by the ice according to this conception of the 

 history of Snowdon was very small in comparison with that involved 

 in the explanation adopted by Professor Davis. In his well-known 

 paper both in the text and in an illuminating sketch (Davis, 1909, 

 p. 307) he represents Snowdon at the beginning of the glaciation 

 as a down-like upland, with gentle slopes and shallow valleys, cliffless, 

 cragless, and without either corries or river gorges. In his paper 

 (1909, p. 282) he describes pre-Glacial Snowdon as " a subdued 



Fig. 7. — Section from Snowdon to Mynydd Mawr through Llyn Cwellyn. 

 The broken hne represents the approximate surface at the beginning of 

 Glacial times, on the hypothesis that the down-like relief has been destroyed 

 by glacial erosion. The areas in solid black represent the amount of solid 

 rock removed on the alternative hypothesis that the valley had been 

 excavated to approximately its present depth by pre-Glacial streams. 



mountain form with dome-like central summit, large rounded spurs, 

 and smooth waste-covered slopes, and with mature valleys drained 

 by steady-flowing streams ". He maintained (ibid., p. 281) that 

 Snowdon was altered during the Glacial period and chiefly by glacial 

 erosion from " a large featured, round-shouldered, full-bodied 

 mountain of pre-glacial time" "into the sharp featured, hollow 

 chested, narrow spurred mountain of to-day ". 



Professor Davis accepts the " late Tertiary " uplift of Snowdon, 

 but considers that this would not have seriously changed its 

 topography, as the only eflect would have been the formation of a 

 few minor gorges (p. 293). This conclusion is based on two arguments, 

 first that Snowdon has no large trunk rivers, and the streams are not 

 sufficiently different in volume to explain why some cut their valleys 

 deeply and others were left as hanging valleys. These arguments 

 would be conclusive if the valleys had been cut by normal consequent 



