1858.] MFRCmSON — NORTHERN HIGHLANDS, ETC. 369 



whitish, and mottled : portions of it have been formerly opened out 

 for marble-quarries. As Mr. Peach detected an Orthoceratite, there 

 is little doubt that future researches in this rock will bring other 

 fossils to Hght. In approaching its summit, the limestone becomes 

 more impure, its uppermost band bearing a peculiar aspect, and 

 intermingled with schist and shale, — some courses resembling vol- 

 canic ash or grit. 



These beds are at once, as at Eribol, overlaid by beds of whitish 

 and pinkish fine-grained quartz-rock ; and thus in one and the same 

 escarpment, and only a mile from the Inn of Inchnadampff, the 

 limestone is seen to be fairly intercalated in the quartzose series ; 

 the last mounts up by Brebeg into the lofty mountains of ConiveaU, 

 which passing to the S.S.W. constitute a range of mountains that 

 extends into Koss- shire. 



On this last occasion we did not foUow the Lower Silurian limestone 

 further to the S.S.W. than Elphin, where, although it is partially 

 changed into a white, hard, compact marble in the vicinity of 

 certain eruptive rocks (syenite, porphyry, &c.), it stiU occupies pre- 

 cisely the same place in the series,-— the lower quartz-rock being 

 seen to sweep down in broad sheets from the Cambrian sandstone 

 mountains of Suilven, Coulmore, and Coul Beg, and to be surmounted, 

 at the base of the limestone hill of Knockin, by the mottled fucoidal 

 shale-bands. 



Durness and Assynt Limestone. — The lower quartz-rock, with its 

 cap of fucoid- and serpulite-beds, is everywhere surmounted, in 

 Durness as in Assynt, by a strong band of limestone, which, under 

 the scrutiny of Mr. Peach, has afforded those organic remains which 

 have enabled us to pronounce unhesitatingly that these rocks are of 

 Lower Silurian age. Hard, marbled, veined, and occasionally divided 

 by joints, this grey limestone is often highly siliceous. Not only 

 does it assume in parts a cherty character, but in Durness it is filled 

 with a profusion of geodes of chert or quartz, which assume fantastic 

 shapes, and weather to a darker exterior than the body of the rock. 



There, in a less well-preserved condition, some of the fossils, 

 which were at first found at one or two spots only, have recently 

 been detected by Mr. Peach in other localities of that extensive 

 parish. The manner in which many of the fossils have been filled 

 with siliceous matter and the manner in which the organic remains 

 weather under such conditions, offer a striking analogy to the aspect 

 presented by North American specimens derived from strata of the 

 same age in Canada, and transmitted by Sir W. Logan. 



In the environs of Inchnadampf, and particularly to the east of 

 that place, the limestone forms noble terraces resting upon the lower 

 quartz-rock, and is clearly overlaid by other quartz-rocks, which rise 

 into Ben More of Assynt and other lofty mountains. The same 

 order is seen at the Bridge of Skiag and other places, the fucoidal and 

 shale beds always occurring in the upper portion of the lower quartz- 

 rock ; whilst on the road to Durness the whole ascending order is 

 exposed, from the old gneiss upwards, when the spectator looks to 



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