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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 6, 



III. Succession of Lower Silurian Quartz-rocks, Limestones, 

 and Schists. 



1. Sutherland to the Isle of Sky e. 



In a former paper, the succession, of Lower Silurian quartz-rocks 

 and limestones upon Cambrian sandstones was traced to the southern 

 confines of the county of Sutherland. In the present memoir we 

 propose to take up the lines where they were then left, and trace 

 them southwards through Ross-shire into Skye. 



Craig-an-Knochan. — The enormous escarpment of limestone that 

 ranges southward from Inchnadainff becomes less in its southward 

 progress, owing to a gradual thinning away of the calcareous strata. 

 The general succession, however, remains the same. These facts 

 are well shown at the watercourse which divides the counties of 

 Sutherland and Ross, where it pours over the cliff of Craig-an- 

 Knochan. This cliff, here from 60 to 100 feet high, is formed by 

 the escarpment of the limestone, and shows along the whole course 

 a clear section of the strata. The road which skirts its base runs 

 upon the white quartz-rock that stretches westward, across a mossy 

 valley, and then ascends for some way up the sides of Coul-more, 

 an enormous denuded mountain-mass of gently inclined Cambrian 

 sandstone. The white quartz-rock is surmounted by brownish 

 beds containing fucoid impressions, these again by a band of white 

 quartz-rock, above which comes a thick white limestone reaching 

 to the summit of the cliff, where it begins to slope below quartzose 



Pig. 2,— Section at Craig-an-Knochan. 



Coul flfore. Road. 



b. Cambrian sandstone and conglomerate. c 3 . Quartz-rock. 



c 1 . Quartz-rock. c 4 . Limestone. 



c*. Fucoid-bed. c 2 . Limestone. d. Gneissose scbist. 



micaceous beds, the whole dipping E. or E.S.E. at 10° to 15°. The 

 details, of course, vary considerably even in the course of a few 

 yards ; but the general order remains the same, the limestone being 

 regularly intercalated between a series of white quartz-rocks below, 

 and a set of quartzose schists ( = the Upper Gneiss of previous 

 papers) above. 



This order continues to be observable until the road deflects a 

 little to the south-east, crossing the limestone, which then plunges 

 below a series of lonely mountain-tarns, and is not again seen until 



