On the Succession of Rocks in the Northern Highlands. 323 



Ross-shire PvHcI Sutherlandshire reposed. At the same time Prof. 

 Nicol hypothetically suggested, that, until the evidence of fossils was 

 more complete, the quartzite and limestone might be considered as 

 the equivalent of the Carboniferous series of the South of Scotland. 

 Another hypothesis, which had been pro])ounded by the late Mr. 

 Hugh Miller, regarded the quartz-rocks and hard limestones of 

 Sutherland merely as the metamorphosed representatives of the Old 

 Red and Caithness series of the Eastern Coast. 



Both of these hypotheses, however, seemed to the author to be 

 quite incompatible with the physical order of the rock-masses in 

 question ; for, according to the observations made long ago by Prof. 

 Sedgwick and himself, the above-mentioned crystalline rocks, in the 

 lower part of which the Durness fossils have recently been found, 

 are the inferior members of the great undulating mass of micaceous 

 and schistose rocks, which, rolling over to Caithness on the east, 

 there constitute the basis out of which the bottom strata of the Old 

 Red Sandstone are chiefly formed. 



Of late, Mr. Peach has, by his untiring perseverance, obtained a 

 still larger collection of fossils from Durness, and in better ])reserva- 

 tion than those found in 1854, and Mr. Salter finds that this collec- 

 tion of well-defined forms comprises genera belongingonly to the Lower 

 Silurian of North America. Hence all doubt is now dispelled ; and 

 the author, following up the suggestions which he offered at the 

 Glasgow Meeting of the British Association, describes in the present 

 paper these rocks and their fossils ; defining the great unfossiliferous 

 conglomerate-masses of Sutherland as of Cambrian age ; the quartz- 

 ites and limestones as Lower Silurian ; and the overlying micaceous 

 and gneissose schists and flagstones as also of Silurian age. 



In the body of the memoir. Sir Roderick, after a brief notice of the 

 " fundamental gneiss," described the " Cambrian red sandstone and 

 conglomerate," alluding to the faithful descriptions by Hugh Miller 

 and Nicol. He also detailed certain subsequent observations of 

 Colonel James and Mr. Peach on the unconformity of these rocks to 

 the overlying quartzites, and on the great dislocations exhibited in 

 these masses ; and he also noticed the discovery of a porphyry be- 

 tween the gneiss and the conglomerate by the latter observer. 



The " Lower Silurian rocks, in the form of quartz-rock, ciystal- 

 line limestone, chloritic and micaceous schists, and younger gneiss," 

 were then described. The fossils from the quartz-rock consist of 

 small annelide tubes now named SerpuUtcs MaccuUochii, and traces 

 of fucoids. These fossils were long ago noticed, but of late they 

 have been traced in beds for great distances by Mr. Peach. The 

 strong band of limestone between two quartz-rocks is estimated by 

 Colonel .lames to lie about 800 feet above the base of the series, 

 and is of great e.\tent. The fossils detected in it have been deter- 

 mined hy Mr. Salter to be Maclurca Petic/iii, spec. nov. (and its 

 curious twisted opcrcuhun), Ophiletu compacla, well known in Canada, 

 Oncoceras, spec, and Orthoarus, a smooth species with a compressed 

 sij)hunclc. Tliey all closely resemble fossils of the Lower Silurian 

 rocks of North America, which range from the Calcifcrous rock up 



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