PROCEEDINGS OF GEOLOGICAL SOCIETIES* 



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that the quartzites of Sutherland and their subordinate limestones were of 

 Lower Silurian age ; and was strengthened in the opinion, which he had already 

 published, that large portions of the crystalline rocks of the Highlands would 

 prove to be the equivalents of Lower Silurian deposits in the south of Scotland. 

 In 1856 Colonel James and Prof. Nicol separately observed the unconformable 

 overlap of the great conglomerates by the quartzite series ; and the latter geologist 

 greatly extended all previous observations, and communicated to the Society a 

 memoir, showing that the old gneiss and its superposed conglomerate, as seen along 

 a very extensive region of the western coast, formed the buttresses upon which 

 all the crystalline quartz-rock and limestone of the western parts of Ross-shire 

 and Sutherlandshire reposed. At the same time Prof. Nicol hypothetically sug- 

 gested, 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 propounded 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 incom- 

 patible 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-men- 

 tioned 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 preservation than those found in 

 1854, and Mr. Salter finds that this collection of well-defined forms comprises 

 genera known hitherto only in 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 quartzites 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 further noticed the discovery of a porphyry between the gneiss 

 and the conglomerate by the latter observer. 



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

 chloritic and micaceous schists, and younger gneiss," were then described. The 

 fossils from the quartz-rock consist of small annelide tubes now named Serpulites 

 Maccullochii, 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 limestones between two quartz rocks is estimated by Colonel James to lie 

 about 800 feet above the base of the series, and is of great extent. The fossils 

 detected in it have been determined by Mr. Salter to be Maclurea Peachii, spec, 

 nov. (and its curious twisted operculum), Ophileta compacta, well known in Canada, 

 Oncoceras, spec, and Orth(Dceras, a smooth species with a compressed siphuncle. 

 They all closely resemble fossils of the Lower Silurian rocks of North America, 

 which range from the Calciferous rock up to the Trenton limestone, both inclusive ; 

 a group especially to be found in the limestones of the Ottawa River in Canada. 



Passing across Ross-shire, in a more southern parallel, from Loch Duich in 

 Kintail, on the west, to the frontier of the Old Red Sandstone on the east, the 

 general succession of rocks was described to be much the same as that in 

 North-west Sutherlandshire, though there are considerable changes of lithological 



