MOUNTAINS 137 



The relative antiquity of our mountains must be 

 decided not necessarily by the geological age of their 

 component materials, but by the date of their upheaval 

 or of their exposure by denudation. In many cases 

 they can be shown to be the result of more than 

 one uplift. The Malvern Hills, for example, which 

 from their dignity of outline better deserve the name 

 of mountains than many higher eminences, bear 

 internal evidence of having been upheaved during at 

 least four widely separated geological periods, the 

 earliest movement dating from before the time of the 

 Upper Cambrian, the latest coming down to some 

 epoch later probably than the Jurassic period. 



The oldest mountain fragments in Britain are those 

 of the Archaean rocks, and of these the largest portions 

 occur in the north-west of Scotland. 1 Most of our 

 mountains, however, belong to upheavals dating from 

 Palaeozoic time, though the actual exposure and 

 shaping of them into their present forms must be 

 referred to a far later period. Two leading epochs 

 of movement in Palaeozoic time can be recognised. 

 Of these the older, dating from before the Lower 

 Old Red Sandstone and part at least of the Upper 

 Silurian period, was distinguished by the plication of 

 the rocks in a dominant north-east and south-west 

 direction, and the effects of these movements can be 

 traced in the trend of the Lower Silurian ridges and 

 hollows to the present day. 



In Wales two types of mountain-form exist — the 

 Snowdon type, and that of the Breconshire Beacons. 



1 A pre-Cambrian group of mountains has been exposed by 

 denudation in the west of Ross-shire. See p. 72. 



