304 The Realm of Nature CHAP. 



than the Highlands, divided from each other by gently slop- 

 ing valleys, and composed mainly of Silurian rocks, although 

 the Cheviot Hills on its southern boundary are largely of 

 igneous origin. 



391. England. The mountainous Lake District of north- 

 western England has been carved by erosion from great masses 

 of Silurian rock, but numerous outbursts of ancient volcanic 

 material have given ruggedness and grandeur to many of 

 the summits. The mountains of North Wales culminating 

 in Snowdon (3570 feet) generally resemble those of the 

 Lake District in their geological structure. They slope in 

 steep terraces to the sea on the west, and dip down more 

 gently to the low plain of England on the east. In South 

 Wales the mountains of circumdenudation are lower, and 

 the Silurian rocks give place to Old Red Sandstone. This 

 is in turn covered by a great expanse of Carboniferous 

 rocks in the south, where the coal-measures come to the 

 surface. Ancient Primary rocks, especially lower Carboni- 

 ferous and Devonian strata, build up the peninsula of 

 Devon and Cornwall, but great intrusions of igneous rock 

 form the hard framework which the sea has wrought into a 

 coast-line vying in grandeur with that of the north-west of 

 Scotland. The band of high land in the north of England 

 known as the Pennine Chain slopes to the sea on the east, 

 adjoins the Lake District on the west, and to the south- 

 west and south gradually spreads out and sinks into the low 

 plain. The hills and dales of this region are carved out of 

 a great anticline of Carboniferous rocks, comprising lime- 

 stones, coal-measures, and grits or coarse sandstones. The 

 crest of the anticline has been denuded down to the grits, 

 while the coal-measures and limestones crop out on the 

 slopes, forming extensive coal-fields. All the rest of England 

 to east and south is occupied by a great low plain built up of 

 Secondary and Tertiary rocks, the elevation of which scarcely 

 anywhere exceeds 600 feet. From this plain the rugged 

 heights of Primary rocks in the west and north rise as from 

 a sea, the whole character of their scenery contrasting 

 with its gentle ridges and low undulations. An irregular 

 line of heights forming a steep escarpment to the west and 



