1 42 ORIGIN OF SCENERY OF BRITAIN 



to its present level, and before some of the ridges, now 

 prominent, had been exposed to the light. 



The Moors and Wolds of Yorkshire present us with 

 a fragment of a tableland composed of nearly horizontal 

 Jurassic and Cretaceous rocks. The Lammermuir 

 Hills and Southern Uplands of Scotland extend as a 

 broad tableland which has been formed on a deeply 

 eroded surface of Lower and Upper Silurian rocks. 



The Scottish Highlands may also be looked upon 

 as the relics of an ancient tableland cut out of highly 

 crumpled and plicated schists. Among the eastern 

 Grampians large fragments of the plateau exist at 

 heights of more than 3,000 feet, forming wide undu- 

 lating plains that terminate here and there at the edge 

 of precipices. In the Western Highlands, the erosion 

 having been more profound, the ridges are narrower, 

 the valleys deeper, and isolated peaks more numerous 

 (p. 1 12). It is the fate of a tableland to be eventually 

 cut down by running water into a system of valleys 

 which are widened and deepened, until the blocks of 

 ground between are sharpened into ridges and trenched 

 into separate prominences. The Highlands present us 

 with far advanced stages of this process. 



In the youngest of British tablelands that of the 

 volcanic region of Antrim and the Inner Hebrides 

 we meet with some of the earlier parts of the change. 

 That interesting tract of our islands reveals a succession 

 of basaltic sheets which appear to have spread over the 

 wide valley between the Outer Hebrides and the main- 

 land, and to have reached southwards beyond Lough 

 Neagh. Its original condition must have resembled 

 that of the lava-fields of Idaho and Oregon a sea-like 



