VOL. XVII (i) SOME GLACIAL FEATURES IN WALES 33 



SOME GLACIAL FEATURES IN WALES 



AND PROBABLY 



IN THE COTTESWOLD HILLS 



BY 

 L. RICHARDSON, P.G.S. 



[Plates VII.-XIL] 

 (Read November i6th, 1909) 



It is well-known that in late Tertiary times there was a 

 glacial period. In certain parts of North Wales the evidence 

 is very obvious, and includes such features as hanging-valleys, 

 striated surfaces, roches moutonn^es, boulders, and perched 

 blocks. The view given in fig. 2, PI. VII., is of the Llanberis 

 Pass, in North Wales, now a classic demonstration-ground for 

 the study of the products of glacial erosion. Therewith com- 

 pare the view given in fig. i, PI. VII., which is of a Rocky- 

 Mountain valley down which a mountain glacier once obviously 

 flowed. 



It is extraordinary what small changes in the average 

 annual temperature would often suffice to cause glaciation of a 

 district again. 



" Thus it has been recently estimated that a fall of but 3° (Fahr.) in the 

 average annual temperature would result in the formation of small 

 glaciers within the area of the Scottish Highlands, while a like fall 

 of 12° within the Lauren tian Lake district of North America would 

 suffice to bring on a period of glaciation." i 



It is held by many that uplift was one of the prime causes 

 of the extension of the area of glaciation. Certainly the intro- 

 duction of the land-surface into colder altitudes would be 



I Prof. W. H. Hobbs, "The Geogr. Joum.", February, 1910, p. 147, 

 D 



