B. Smith — Glacial Gravels of Corwen. 



313 



alluvium. But just as the highest terraces of the Trent valley 

 between Newark and Nottingham * have been shown to be late- 

 Glacial, so also the highest terraces of these mountain valleys are 

 now recognized as having been formed during the retreat of the ice. 

 They are the equivalents of the present day sheets of gravel fornn d 

 alongside, and at the snouts of, the retreating valley-glaciers of the 

 Yakutat Bay region of Alaska. 



Map showing site of Gravel Plain near Corwen. 

 In broad open valleys, like that of the Trent, the late-glacial 

 terraces are of fairl)' regular height and level surface; but in 

 mountain valleys, such as those of the Tanat and Vyrnwy, they 

 appear at various heights above the recent alluvium — here 20 feet, 

 there 40 feet — even when the remnants of a dissected terrace are 



1 Geology of the Country between Neivark and Nottingham (Mem. Geol. 

 Surv.), 1908, pp. 73-6. 



