1 40 ORIGIN OF SCENERY OF BRITAIN 



that time, otherwise, the denudation, vast as it is, 

 would probably have been still greater. Not improb- 

 ably the region had become stationary at a base-level 

 of erosion beneath the sea ; that is, it lay too low to 

 be effectively abraded by breaker-action, and too high 

 to become the site of any important geological forma- 

 tion. The present ridges and valleys of the High- 

 lands are entirely the work of erosion. When they 

 began to be traced, the area probably presented the 

 aspect of a wide undulating tableland. Since that early 

 time the valleys have sunk deeper and deeper into 

 the framework of the land, the ridges have grown 

 narrower, and the mountains have arisen, not by up- 

 heaval from below, but by the carving away of the rest 

 of the block of which they formed a part. In this 

 evolution, geological structure has played an important 

 part in guiding the erosive tools. The composition of 

 the rock-masses has likewise been effective in determin- 

 ing the individuality of the mountain-forms. 



The mountains of Ireland are distributed in scattered 

 groups round the great central plain, and belong to at 

 least three geological periods. The oldest groups prob- 

 ably took their rise at the time of the older Palaeozoic 

 upheaval, those of the north-west being a continuation 

 of the Scottish Highlands, and those of the south-east 

 being a prolongation of those of Wales. Later in date 

 as regards the underground movements that determined 

 their site, are the mountainous ridges of Kerry and 

 Cork. These are local uplifts which, though on a 

 small scale, are by far the best examples in Britain of 

 true mountain-structure. The Old Red Sandstone 

 and Carboniferous rocks have there been thrown into 



