886 TUE BRITISH ISLES. 



moved have been carefully mapped, and they show that the ice travelled outwards 

 from a great central snow- Held whieli extended obliquely across the country, 

 from the mountains of Conncmara to tlie plutoau of Antrim. To the north 

 of this field of snow, which included the plateiui of Magheraboy, with its hills 

 grouped like the ribs of a fan, the groovings and striations are towards the north- 

 west, whilst on the opposite slope their direction is south and south-west, except 

 where the course of the ice was impeded or deflected by local mountain barriers. 

 The sheet of ice which at that period covered the plains of Ireland had a thickness 

 of 1,000 feet.* 



But long before the ice planed and levelled vast tracts of the surface of Ireland, 

 the action of the water, operating through untold ages of our planet, had swept 



Fig. 195.— The Table-land of Magheraboy. 

 Sc.'ile 1 : 200,000. 





=f^:M 



r i;Ktnvt'f^oS\M-: 



ji' 



i. 



7^ 



2 Miles. 



away a considerable portion of the surface strata. The plain which occupies 

 nearly the whole of the centre of the island is a proof of this. The extent of this 

 plain coincides pretty nearly with that of the carboniferous limestone, but the 

 coal measures of this formation have been removed, and there remain as it 

 were merely the foundations of the ancient edifices. Only here and there, in 

 well-sheltered localities, a few shreds of the coal-bearing strata which formerly 

 overspread so large a portion of the island still exist. The agents of denuda- 

 tion which deprived Ireland of her upper carboniferous strata were operative 

 * Maxwell Close, " Glaciation of Ireland ; " Hull, " Physical Geologj- and Geography of Ireland." 



