xv The Continental Area 303 



places. Mountains, below the height of 3000 feet at least, 

 have acquired a more or less flowing outline through glacial 

 grinding ; and the low land has been largely enveloped in 

 boulder clay and similar accumulations. 



390. Scotland. On the map of vertical relief (Plate 

 XVI.), the northern part of Great Britain is seen to be 

 divided into three natural regions stretching across the 

 island from north-east to south-west. Most of the area 

 north-west of a line drawn from the Firth of Clyde to 

 near Aberdeen is occupied by the Highlands. This is 

 an old plateau, largely composed of crystalline schistose 

 rocks, and pierced by many granite -like masses. The 

 heights, separated by deep valleys, are rugged and 

 often precipitous, crowned by crests of splintered rock. 

 The Highlands are divided into a northern and a south- 

 ern group by the Great Glen which unites the Moray 

 Firth with the Firth of Lome, and contains Loch Ness and 

 Loch Lochy, two long narrow fresh -water lakes. The 

 highest point of Great Britain is the mass of Ben Nevis 

 (4400 feet), near the south-western extremity of the Great 

 Glen, but a greater area of scarcely lower elevation occurs 

 round Ben Macdhui. South of the Highlands stretches a 

 broad low plain the Midland Valley diversified by lines 

 of hills like the Pentlands, Ochils, and Sidlaws, and isolated 

 precipitous crags such as those occupied by the castles of 

 Dumbarton, Stirling, and Edinburgh. These abrupt heights 

 are due to masses of hard volcanic rocks formed in the Car- 

 boniferous period or later, and now exposed by the more 

 rapid erosion of the softer strata which had buried them. 

 Along the border of the Highlands there is a strip of Old 

 Red Sandstone sharply separated from the crystalline schists, 

 slates, etc., by the Great Fault which runs from the Firth of 

 Clyde to near Aberdeen. Along the southern edge of the 

 plain a similar strip of the same formation is terminated 

 by a line of faults stretching from near Ayr to near D unbar. 

 Carboniferous strata with the coal-measures cropping out 

 in several places occupy the centre of the Lowland Valley. 

 The Southern Uplands, which form the third division, are 

 a group of rounded grassy and often peat-topped hills, lower 



