THE CRYSTALLINE SCHISTS OF THE HIGHLANDS. 415 



Ben Capuill near Tighnabruaich. This he believed to be a true anticline 

 of the bedding. The altered basic rocks he calls greenstones and points out 

 their intrusive origin. 



In 1861 Murchison and Geikie 1 described certain sections along the margin 

 of the southern Grampians with reference to the supposed succession of the 

 rocks in northwest Sutherlandshire. They believed that the southern and 

 central Highlands were overlaid by a great series of quartzites, limestones, 

 and schists, the representatives of those in the northwest, and that they 

 always bore the same relative position to one another, namely the quartzites 

 at the base, followed by limestones, and the whole overlaid by the schists sup- 

 posed to be of Silurian age. In another paper about the same date these authors 

 maintained, in opposition to the views advanced by Sharpe, that the foliation 

 of the Highland rocks generally coincided with or followed the original 

 planes of sedimentary deposition. In the same year similar views to these 

 were advanced by Harkness 2 as to the rocks south of the Caledonian Canal. 



In 1863 the next contribution to the study of these rocks appeared from 

 the pen of James Nicol, 3 and was, in many respects, as I have elsewhere 

 pointed out, the most far-seeing paper which has ever been written on the 

 subject. He entirely discarded the hypothetical views of Murchison, Geikie, 

 and Harkness. Taking a series of sections across the Highland frontier he 

 noted the occurrence in them all of a regular order of clay-slates, grits, grey- 

 wackes, and quartzites. He also remarked the reversal of dip from S.E. to 

 N.W. as he proceeded from west to east across the Highland frontier, and 

 arrived at the conclusion that the slates along the Firth of Clyde were in 

 their normal position overlying the schists of the interior, w^hereas these 

 further east as in Perthshire, with a N.E. .dip and thus apparently under- 

 lying the schists of the interior, did not really do so, their position being 

 really due to a reversal of the beds. This reading is, however, apparently 

 incorrect, the Perthshire slates being really in their normal position, while 

 they are reversed along the Firth of Clyde. Nicol also pointed out the 

 existence of a highly contorted belt on both sides of Loch Long, and strenu- 

 ously maintained that the central Highland quartzites belonged to a horizon 

 higher than the schists further south, and did not underlie them as had been 

 maintained by Murchison and Geikie. 



In 1891, in a Presidential Address to the Geological Society, Sir A. Geikie 4 

 gave a table of the Highland rocks, the work of the Geological Survey, and 

 placed the Central Highland quartzite at the top, and the phyllites and grey- 

 wackes of the Pass of Leny at the base of the series. Independently a 

 similar succession was advocated the same year by Henry Coates and the 

 author of this paper. In 1896 the author 5 arranged the clastic rocks of the 

 Highlands iii descending order as follows : Upper Arenaceous zone, Upper 

 Argillaceous zone, Middle Arenaceous zone, Loch Tay Limestone zone, Lower 

 Arenaceous zone, and Lower Argillaceous zone. The principal lithological 

 features and geographical position of each zone was first given, then a series of 

 sections illustrative of their succession and physical structure in Highland 

 Perthshire, and it was pointed out that along the shores of the Firth of Clyde 

 the zones forming the frontier Highlands have been bent into a deep 

 synclinal fold with a reversal of dip. 



In 1897, in a Memoir upon the Geology of Cowal, 6 published by the 

 Geological Survey, a series of schist-zones, beginning at the great boundary 



1 "The Altered Rocks of the Western Islands of Scotland and the Northwestern and 

 Central Highlands," Quart. Journ. Geol. Soc., 1861, vol. xvii., p. 171. 

 -Quart. Journ. Geol. Soc., 1861, vol. xvii., p. 256. 

 * Ibid., 1863, vol. xix., p. 180. 

 *Ibid., 1891, vol. xlvii., p. 74. 



5 Geological Magazine, 1896, vol. iii., p. 167 and p. 211. 

 6 "Geology of Cowal," Mem. Geol. Survey, 1897. 



