502 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 3, 



conviction (at the British Association, Glasgow Meeting, 1854) 

 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 cry- 

 stalline rocks of the Highlands would prove to be the equivalents 

 of the Lower Silurian deposits in the South of Scotland. In 1856 

 Colonel James and Prof. Nicol separately observed the unconform- 

 able 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 exten- 

 sive 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 Sutherland 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 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. 



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

 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 preserva- 

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

 tion of well-defined forms comprises genera belonging only 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 of it 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 between the gneiss and the conglomerate by the latter 

 observer. 





