20 



GLACIAL DRIFT, ETC. 



Uppeb underneath the present sea level to a height of about 2 300 



feet on some of the mountains. 



Near the shore it has 



iiiEecess 41. sometimes been re-arranged and waterworn by the sea during 



terrestrial oscillations of level, but in the higher grounds it 

 is generally in its native state, consisting of clay, angular 

 stones, and boulders. Shells Avere found by Mr. Trim- 

 mer, on Moel Try fan, 1,300 feet above the sea, in gravel, and 

 others were found by myself in a boulder clay at about the 

 same height, less than two miles west of the peak of Snowdon. 

 It has been already stated that some of the Welsh glaciers 

 shed their moraines in the sea, while drift was beino- de- 



posited on neighbouring sea bottoms. Much of this drift 

 precisely resembles ordinary moraine matter in the appear- 

 ance and quality of its mud, and the angularity, scratched 

 surfaces, and sizes of its stones. At a time when glaciers 

 descended to the sea, the higher mountains rose as islands 

 of not more than about 2,000 feet high, and yet gave birth to 

 distinct glaciers. It is therefore not impossible that in 

 other portions of the same islands not possessed of the form 

 requisite to originate massive glaciers, snow and ice may 

 yet have covered nearly their entire surfaces, for unless 

 the cold were sufficient to produce such a result, it is 

 difficult to understand how on other parts of these small 



then certainly filled 



islands 



good-sized glaciers, such as 



If this covering 



the valleys, could have been produced, 

 did exist, it is very intelligible how the drift on the sides 

 of the mountains is generally composed of stones from the 

 hills close above, and also is entirely moraine-like in its 

 character. It is not till we reach the comparatively dis- 

 tant lower ground of Caernarvonshire, near the sea, and 

 the plains of Anglesea, that far travelled fragments begin 

 to occur in ordinary drift deposits. Under any circum- 

 stances, small bergs and coast-ice grating along the shores 

 would in the course of time be sufficient not only to polish 

 the rocky coasts, but also to groove and scratch blocks and 

 stones imprisoned in floating ice, such as are shown in the 

 following specimens. 





H> 



