122 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 1, 



through Skiddaw illustrate this district ; No. 1 shows the position 

 of strata, and No. 2 the dip of the planes of cleavage, along the same 

 line of section from the mountain limestone of Uldale on the north to 

 the middle of Borrowdale, where a change of dip of the beds indicates 

 the commencement of another area of elevation. 



The axis of this northern area consists of the sienite of Carrock 

 Fell and of sandy bands and dykes of igneous rocks of various cha- 

 racters running to the westward nearly as far as the foot of Bassen- 

 thwaite Water ; on both sides of this axis the beds of slate dip away 

 from the igneous rocks at nearly the same angle. 



From the anticlinal axis at Carrock Fell to Rossthwaite in Borrow- 

 dale, the beds dip constantly to the southward (between S. 15° E. and 

 S. 30° E.) ; the distance is twelve miles, which is the semidiameter of 

 the area of elevation. The series of beds, commencing with the 

 lowest, is as follows : — 



1. Skiddaw Slate, viz. — 



a. Black clay-slate with crystals of chiastolite in all the northern 

 half of Skiddaw and Saddleback : the chiastolite seems to be due to 

 the neighbouring igneous agency, as the western continuation of the 

 same beds near Bassenthwaite consists of soft brown clay-slate with- 

 out chiastolite. In Skiddaw these beds dip S. 30° E. 45°, and the 

 cleavage coincides both in dip and strike with the bedding. 



h. Hard black clay-slate, forming the northern part of Skiddaw, 

 where it dips S. 30° E. 30°, with a cleavage which dips S. 30° E. 50°. 



c. Rotten dark brown clay-slate, with layers of ferruginous clay 

 nodules approaching a clay ironstone. This forms the lower hill of 

 Latrigg and the valley of Keswick : the beds dip S. 30° E. 30°, and 

 the cleavage dips S. 30° E. 60°. 



2.. Green slate, which overlies the Skiddaw slate in the first high 

 hills on the sides of Derwentwater. It is usually either a hard gritty 

 siliceous rock of a light grey colour, unfit for use as slate, or a roofing- 

 slate of light greenish tint, somewhat approaching steatite in its softer 

 beds, and containing numerous plates of dark green indurated talc on 

 the surface of the planes of cleavage. Many beds are brecciated, the 

 foreign masses usually consisting of slate differing in colour and hard- 

 ness from the matrix. On the line of the sections Nos. 1 & 2, the 

 green slate is interrupted by two bands of porphyry, which alter the 

 character of the slates near them without disturbing the direction of 

 the beds or cleavage : one of these bands crosses Derwentwater near 

 its head, the other crosses Borrowdale at the Castle Hill. 



At the side of Derwentwater the green slate dips about S. 30° E. 30°, 

 the cleavage dipping S. 1 5° E. 70°. A little way up Borrowdale the slate 

 is quarried on a large scale, it here dips S. 15° E. 30°, and the clea- 

 vage dips S. 15° E. 75° ; near Rossthwaite the beds dip S. 15° E. 25°, 

 and the cleavage dips S. 15° E. 85° : just beyond this spot the dip of 

 the beds changes to the west of north, and the cleavage is perpendi- 

 cular with a strike of N. 65° E. The line which separates the two 

 great areas of elevation of the Lake Mountains passes here, and the 

 position of the beds to the south of it must be explained by examining 

 the forces which have acted farther south. 



