380 EECEXT WOEK OF THE GEOLOGICAL STJRYET 



that the red sandstones and conglomerates rest unconformably on 

 the western gneiss, and that, in Sutherland, they are overlain by 

 quartz-rocks and limestones, which alternate with and are suc- 

 ceeded by gneiss and schists forming the chief portion of the 

 Highlands of Scotland. He chronicled the important discovery of 

 worm- tubes (named by Salter Serpulites MaccullocMi) and Orthocera- 

 tites in the quartz-rock of Loch Eriboll*. 



In 1841 Hay Cunningham confirmed ITaccuUoch's observations 

 regarding the unconform ability between the red sandstones and 

 the underlying gneiss, and the occurrence of an upper gneiss 

 resting on the quartz-rocks and limestones. He further corrobo- 

 rated the discovery of organic remains in the quartz-rock, and 

 stated that "there are gneisses and mica-slates that have been 

 elaborated after these were called into being "f. 



In 1852 a suggestive memoir was published by Mr. Daniel 

 Sharpe on the foliation of the rocks of the Xorthern Highlands, in 

 which he endeavoured to show that foliation is the ultimate stage 

 of cleavage. He distinguished between the gneiss lying east and 

 west of a line drawn from Loch Eriboll to the head of Loch 

 Maree, the foliation and cleavage of the western area and of Lewis 

 striking I^.W. to S.E., and that of the eastern area striking S.W.J 



The discovery of fossils in the Durness Limestone, in 1854, by 

 Mr. C. W. Peach §, imparted fresh interest to these rocks, and led 

 Sir E-oderick Murchison to revisit the north-west Highlands, 

 which he had seen with Sedgwick as far back as 1827. He invited 

 Professor Xicol to accompany him, and the two observers went 

 over some of the northern sections together in the autumn of 1855. 

 At the British Association meeting of that year Murchison spoke 

 guardedly of the age of the limestones of Sutherland, but was 

 evidently inclined to regard them as Lower Silurian, the fossil 

 evidence not having j'ct proved decisive on that question. Next 

 year N'icol returned to the ground and extended his observations. 

 He detected a marked unconformability between the red sandstones 

 and quartz-rocks, which he traced for upwards of a hundred miles. 

 At the same time he was led to the conclusion that the red sand- 

 stones of the west of Sutherland and Eoss-shire were probably of 

 Devonian age, and the quartzite and limestone Lower Carboniferous. 

 When, in the following year, Peach found better-preserved fossils, 

 which put the Lower Silurian horizon of the limestones beyond 

 doubt, I^icol, abandoning the suggestion he had put forward as to 

 the geological age of the rocks, applied himself with renewed energy 



* ' A Description of the Western Islands of Scotland,' vol. i. pp. 1-234, 

 243, 295 et seq., vol. ii. pp. 89, 104, 508, 515, &c. ' A Geological Classification 

 of Eocks,' London: p. 333. "Supplementary Eemarks on Quartz-Rocks," 

 Trans. Geol. Soc. ser. 2, vol. i. pp. 53-60. ' A System of Greology,' vol. ii. 

 •chap. 29. 



t " Greognostic Account of the County of Sutherland," Trans. Highl. Soc. vol. 

 xiii. p. 73. 



I " On the Arrangement of the Foliation and Cleavage of the Eocks of the 

 Xorth of Scotland," Phil. Trans, vol. cxlii. p. 445. 



§ " Notice of the Discovery of Fossils in the Limestone of Durness," Proc. 

 Roy. Phys. Soc. Edinh. (1885), vol. i. p. 23. 



