CHAPTER XVIII. 



THE PHYSICAL STRUCTURE OF SCOTLAND THE HIGHLANDS 



THE GREAT VALLEYS OF THE FORTH AND CLYDE THE 



LAMMERMUIR, MOORFOOT, AND CARRICK HILLS. 



I NOW come to that part of the subject in which it will 

 be my duty to explain the connection between the 

 geological phenomena of Britain and the nature of its 

 modern scenery. In this chapter I shall briefly describe 

 the most mountainous part of Britain, and tell why great 

 part of Scotland is so rugged. In another chapter I 

 shall have to show that there is a strong contrast be- 

 tween the physical features of Scotland, and those of 

 the middle and east of England, and to explain why 

 the conformation of these two districts, and those of the 

 east and west of England, are essentially so distinct. 



In Scotland gneissic rocks and granites are exten- 

 sively developed. The north-west coast of Sutherland, 

 and the outer Hebrides, chiefly consist of the oldest known 

 formation, called Laurentian, as already stated in Chap- 

 ter V. Above them, in Sutherland, there are unaltered 

 red or purple Cambrian sandstones and conglomerates, 

 which lie unconformably on the Laurentian gneiss. In 

 fact, the Laurentian strata were disturbed, metamor- 

 phosed, and much wasted by denudation, before the de- 

 position of those Cambrian strata began, and fragments of 

 the denuded gneiss help to make up the conglomerates. 

 The Lower Silurian rocks come next in the series, and 



