168 



MAN AND THE GLACIAL PERIOD. 



country to be due to the thick mask of glacial deposits 

 which obliterates the harsher features of the solid rocks. 



" The deposits on Moel Tryfaen are exposed in a slate- 

 quarry on the northern aspect of the hill near the summit, 

 and consist of two wedges of structureless boulder-clay, 

 each thinning towards the top of the hill. The lower mass 

 of clay, wherever it rests upon the rock, contains streaks 

 and irregular patches of eccentric form, of sharp, perfectly 

 angular fragments of slate ; and the underlying rock may 

 be seen to be crushed and broken, its cleavage-laminae 

 being thrust over from northwest to southeast — that is, 

 up-hill. The famous ' shell-bed ' is a thick series of 

 sands and gravels interosculated with the clays on the 

 slope of the hill, but occupying the entire section above the 

 slate towards the top. The bedding shows unmistakable 

 signs of the action of water, both regular stratification and 

 false bedding being well displayed. The stones occurring 

 in the clays are mainly if not entirely Welsh, including 

 some from the interior of the country, and they are not in- 

 frequently of large size — two or three tons' v/eight — and 

 well scratched. 



" The stones found in the sands and gravels include a 

 great majority of local rocks, but besides these there have 

 been recorded the following : 



Eock. 



Source. 



Highest 



point 

 in situ. 



Minimum 



uplift 

 in feet. 



Granite 



Eskdale, Cumberland. . . 



Criff el, Galloway 



Antrim (?) 



1,286 

 "l,666 



1,097 



64 



Granite 





Flint 



350 



To these I can add : 

 Granophyre 



Buttermere, Cumber- 

 land 









Eurite * 



Ailsa Craig, Frith of 

 Clyde 







253 









* The altitude at which this rock occurs on Ailsa Craig has not 

 been announced, so 1 have put it as the extreme height of the island. 



