TRANSACTIONS OF SECTION C. 619 



contact alteration, black and yellow cherts, jaspers with spherulitic structures 

 which indicate that they have been formed by the silification of liparites of the 

 ' Lea-rock ' type and spherulitic felsites that bear a striking resemblance to those 

 of Uriconian age in Shropshire. These interesting relics have been derived from 

 formations which do not now occur anywhere in the western part of the counties 

 of Sutherland and Ross, and they furnish impressive testimony of the denudation 

 of the Archaean plateau in pre-Torridonian time. 



These Torridonian sediments, like the sandstones of younger date, contain lines 

 of heavy minerals, such as magnetite, ilmenite, zircon, and rutile.' The dominant 

 felspar of the arkose group is microcline, that of the basal group oligoclase. In 

 the "calcareous sediments of the upper and lower groups fossils might naturally be 

 expected, but the search so far has not been very successful. Certain phosphatic 

 nodules have been found in dark micaceous shales of the upper group which have 

 been examined by Mr. Teall. From their chemical composition these nodules 

 might be regarded as of organic origin ; but he has found that they contain 

 spherical cells with brown-coloured fibres, which appear to be debris of organisms.- 



Early in last century the Torridonian deposits were referred by Macculloch ^ 

 and Hay Cunningham* to the 'Primary Red Sandstone,' and by Murchison,^ 

 Sedgwick, and Hugh Miller to the Old Red Sandstone. The structural relations 

 of the Torridon Sandstone to the overlying series of quartzites and limestones 

 were first clearly shown by Professor Nicol," who traced the unconformability 

 that separates them for 100 miles across the counties of Sutherland and Ross. 

 When Salter pointed out the Silurian facies of the fossils found in the Durness 

 limestone by Mr. Charles Peach, the Torridonian formation was correlated with 

 the Cambrian rocks of Wales by Murchison.^ The discovery of the Olenellus 

 fauna, indicating the lowest division of the Cambrian system, in the quartzite- 

 limestoce series by the Geological Survey in 1891 "^ demonstrated the pre-Cambrian 

 age of the Torridon Sandstone. In view of that discovery, which proves the 

 great antiquity of the Torridonian sediments, it is impossible to climb those 

 picturesque mountains in Assynt or Applecross without being impressed with 

 the unaltered character of these deposits. Yet it can be shown that under the 

 influence of post-Cambrian movements they approach the type of crystalline 

 schists. 



iiefore proceeding to the consideration of the Durness series of quartzites and 

 limestones and their relations to the Eastern Schists, brief reference must be 

 made to the controversy between Murchison and Nicol regarding the sequence of 

 the strata. 



The detailed mapping of the belt between EriboU and Skye by the Geological 

 Survey has completely confirmed Nicol's conclusions (1) that the limestone is 

 the highest member of the Durness series; (2) that the so-called 'Upper Quartzite' 

 and ' Upper Limestone ' of Murchison's sections are merely the repetition of the 

 lower quartzite and limestone due to faults or folds ; (3) that there is no con- 

 formable sequence from the quartzites and limestones into the overlying schists 

 and gneiss ; (4) that the line of junction is a line of fault indicated by proofs of 

 fracture and contortion of the strata. It is true that in the course of his investi- 

 gations Nicol's views underwent a process of evolution, and that even in the form 

 in which he ultimately presented them he did not grasp the whole truth. We 

 now know that he was in error when he regarded portions of the Archsean gneiss, 



' Annual Report of the Geological Survey for 1803, p. 263. 



= Ihid., 1899, p. 185. 



' Trans. Gcol. Soc, ser. 1, vol. ii. p. 450 ; The Western Jslei of Scotland, vol. ii. 

 p. 89. 



" Transactions of the Higliland and Agricultvral Society of Scotland, vol. xiii. 

 (1839). 



* Trans. Qeol. Soc., ser. 2, vol. ill. p. 155. 



" Quart. Jonrn. Geol. Soc., vol. xiii. p. 17. 



' Ihid., vol. XV. p. 353. 



" Ibid., vol. xlviii. p. 227. 



