356 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 1, 



mountains. Aware that Col. James, R.E., was about to visit that 

 region early in the summer of 1856, to select a site for the purpose 

 of observations on the density of the earth, I requested him to trace 

 that line of junction. This he did successfully as regarded the moun- 

 tains of Suilven and Queenaig, and showed, in a letter to myself, 

 that the red conglomerate and sandstone were unconformahly over- 

 lapped by the quartzite series. Later in the same summer of 1856, 

 Professor [N^icol greatly extended our previous observations, and drew 

 those clear sections which are published in the Journal of the Geolo- 

 gical Society*, showing that the old gneiss and its superposed con- 

 glomerate, as seen along a very extensive region of the Western Coast, 

 formed really the buttresses upon which all the crystalline quartz- 

 rock and limestone of the western parts of Ross-shire and Suther- 

 landshire reposed. 



It was thus that the very high antiquity of the red conglomerate 

 and sandstone of the whole of the N.W. Coast was determined ; for 

 not only was it shown to underlie strata which, as I had suggested, 

 would pi'ove to be of Lower Silurian age, but the edges of such 

 subjacent conglomerate and sandstone were seen to have been eroded 

 before such Silurian deposits had been laid upon them. 



Having agreed with me as to the facts respecting the ascending 

 order of, 1st, an underlying or old gneiss ; 2nd, great red conglomerate 

 and sandstone ; and, 3rd, the quartzites and limestone with overlying 

 gneissose rocks, — Prof. Nicol, influenced by the mineral analogy of a 

 fossiliferous limestone being intercalated in quartzites which he 

 rightly considered to be merely altered sandstones, suggested, theoreti- 

 cally, that these quartzose and calcareous rocks might prove to be the 

 equivalents of the Carboniferous series of the south of Scotland, in 

 which limestones are also enveloped in sandstones. But my associates 

 will recollect that my fellow-labourer (than whom no man is more 

 impressed with the desire to ascertain the whole truth) simply put 

 forth this hypothesis until aU doubt should " be removed by the 

 discovery of better-preserved characteristic fossils f." 



In thus speculating. Prof. Mcol thought that the imperfect fossils 

 on which I had reasoned were inadequate grounds for my hypothesis. 

 He was also unconvinced of the accuracy of my inference, as based 

 upon a datum which I held to have been fiied long before by 

 Sedgwick and myself, and to which I still adhere, viz. that the 

 above-mentioned crystalline rocks, in parts of which the fossils 

 have recently been found, are the inferior members of the great 

 undulating mass of gneissic and micaceous rocks, which, rolling over 

 to the East Coast, there constitute the basis out of which the bottom 

 strata of the deposit known as " the Old Red Sandstone " are chiefly 

 formed. Though still sceptical on this latter point, and waiting 

 for a more accurate survey of the country than has hitherto been 

 made. Prof. Nicol bows now to the fresh evidences of organic remains, 

 and considers, with myself, that the quartz-rocks and limestones of 

 the west of Sutherland are of Lower Silurian age. 



^ Vol. xiii. p. 23. 



t See Nicol, Quart. Journ. Geol. Soc. vol, xiii. p. 36. 



