Ch. VII.] GRANITIC AND SCHISTOSE ROCKS. 121 



Mr. Weaver*, " rises in bold granitic precipices above Augh- 

 avanagh, and is capped with mica-slate, which occupies its 

 summit and a considerable part of its western declivity; 

 while the steep brows around this mountain, its precipitous 

 sides towards Glenmalur on the east, and towards the glen of 

 Imale on the north, and its long southern arm, consist of 

 granite. This cap of mica-slate is also partly interstratified 

 with beds of granite, and these alternations are sometimes 

 traversed by veins of granite. The summit of this mountain 

 forms a kind of table land, presenting a smooth green sod, 

 and is strongly contrasted with many of its neighbours." 



This cap of mica-slate appears to be a continuation of the 

 main mass which forms inlets in the adjacent glens : but the 

 picturesque summit of Cadeen consists of a shield- shaped mass 

 of mica-slate, for granite occupies the foot in every direction .f 



In tracing the slate near its junction with the granite, in 

 Cornwall, it will be found, in consequence of its undulations, 

 sometimes to rise high on the side of the granite ; and again, 

 at a short distance therefrom, to sink to a much lower level, 

 where it lies concealed under several layers of recent deposits, 

 such as alternating beds of gravel, debris, and vegetable 

 remains, which, when tin ore is present, are provincially known 

 by the name of stream- ivorks. This undulating line is not 

 only higher and lower, at any one part, according to the con- 

 vexity or concavity of the curve, but the whole line is found 

 to decline gradually from N. E. to S. W., so that the slate 

 which, in the eastern part of the county, attains to 1000 

 feet in height, is, at the Scilly Islands, below the present sea 

 level. This statement is, however, only correct as a general 

 view ; for, at many intermediate points, between the begin- 

 ning and termination of this curved line, the slate will be 

 found more elevated than in places which lie more to the 

 north-east ; as is also the case as regards the relative altitudes 

 of the highest points of the granitic range which traverses 



* Geol. Trans, vol. v. p. 153. f Idem, p. 160. 



