Ch. VII.] GRANITIC AND SCHISTOSE ROCKS. 119 



CHAPTER VII. 



ON THE RELATIVE POSITION, AND ON THE NATURE OF THE 

 GRANITIC AND SCHISTOSE ROCKS AT THEIR JUNCTION. 



Position of the primary schists next granite. They extend far over this rock 

 through the transverse valleys in Cornwall. The mica-slate of Ireland 

 similarly situated, capping the granitic mountain of Lugnaquilla. The 

 Cornish strata skirt the granite in an irregularly undulating curve. The 

 same arrangement obtains in the isle of Arran, in the north of Scotland, 

 and in the Alps. Dip of the strata at the junction, in Arran, in Corn- 

 wall, in Galloway, apparently irregular not so dependent on the 

 structure of the primary rocks illustrated by sections. The anticlinal axis 

 of primary districts said to be simple in each geographical range not so 

 in the Ocrynian range, nor in the Pyrenees. Composition of granite and 

 primary schists at their junction, in Cornwall, near Cherbourg, in Ireland 

 in lona and Mull, in Glen Tilt, and near St. Paul Fenouilletin the 

 Pyrenees. 



IT has been already stated that the primary rocks have an un- 

 dulated structure ; and, that the curvatures of these rocks cross 

 each other at right angles, thus producing, at the surface, two 

 parallel systems of valleys. If we examine those valleys, in 

 Cornwall, which are at right angles with the central range, it 

 will be frequently found that the schistose rocks run up there 

 to a considerable distance, forming, as it were, bays and inlets 

 on the sides of the large insulated masses of granite: sometimes, 

 indeed, these intruding beds of slate meet from opposite sides, 

 and thus cut off patches of granite from the main masses. In 

 this manner the Tregonning and Godolphin Hills are separated 

 from the granitic hills of Crowan and Wendron, by the inter- 

 vention of a narrow valley of slate : and even the hollow, 

 which divides the former hills from each other, appears to be 

 superficially covered with a schistose rock. It has been lately 

 ascertained that the granitic mass of Kingston Down is not 

 continuous at the surface, as laid down in the map, but is also 



