1848.] SHARPE ON SLATY CLEAVAGE. 125 



the northern area ; and the position of the planes of cleavage is as 

 complicated as that of the strata. It would be tedious to go into 

 these disturbances in detail, but we must glance over them, as they 

 show how the position of the cleavage-planes has depended on the 

 eruptive forces which have elevated and disturbed the strata, and thus 

 confirm the opinion that the cleavage is due to mechanical causes. 



The most complicated part of this area is that occupied by the 

 green slates which has been broken through by several bands of por- 

 phyritic rocks : these have modified the arrangement both of the strata 

 and of the cleavage, and have influenced the physical geography, so 

 that we must first examine their position on the line of country 

 crossed by the sections. 



Commencing on the north, the first great band of porphyry seen on 

 section 3 is that of Greenside, on the north side of Glenridding, which 

 forms the limit of the section, and belongs to the northern area of 

 elevation just described : the general direction of this band is east 

 from the southern part of Derwentwater to the southern part of 

 Ulswater. 



The Greenside porphyry is succeeded by the slates of Helvellyn, 

 the line between them being well marked by a great fault running 

 down Free Mosedale and the lower part of Glenridding : throughout 

 Helvellyn the slate is more or less crystalline, but both the cleavage 

 and the bedding are well seen. In Kaise and Whiteside the slate 

 dips N. 15° W. 75°, its cleavage dipping S. 15° E. 85°: there is a 

 fault at the head of Glenridding forming an anticlinal axis on which 

 the cleavage is perpendicular and strikes with the beds ; beyond that 

 fault in the higher parts of Helvellyn, the slates dip S. 25° E. 30° to 

 35° ; the cleavage dips close to the fault S. 25° E. 75° ; but its eleva- 

 tion gradually increases to the southward, and it is again perpendi- 

 cular on the south side of Helvellyn High Man where another fault 

 occurs, at which the beds form a synclinal axis : in the Eagle Crag 

 the slate is more crystalline, and dips N. 25° W. 30°, resting on the 

 porphyry of Grisedale Head. In the Eagle Crag the cleavage dips 

 N. 25° W. 85°, and at the junction of the slate and porphyry N. 25° 

 W. 80°. 



The band of porphyry which crosses the country south of Helvel- 

 lyn is about two miles wide : on the line of section 3, it divides the 

 waters of Cumberland and Westmoreland at the ridge of which 

 Dunmail Raise is a part : its general direction is east. At the south 

 end of Raise Gap, it is succeeded by a metamorphic slate with a 

 cleavage dipping N. 20° W. 70°, in which the traces of bedding can 

 hardly be distinguished ; this crosses the Keswick road about 1^ 

 mile north of Grasmere. 



South of the metamorphic slate we find another great band of 

 porphyritic rock nearly a mile and a half wide, which reaches to the 

 banks of Grasmere : on section 3, this rock has a faint but regular 

 cleavage dipping N. 40° W. 80°, so that we might be tempted to 

 regard it as a slate rock of which the bedding has been obliterated, 

 and the structure rendered crystalline by igneous agency below the 

 surface. But farther east, the same band forms the summit of the 



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