proceediiJgs ov geological societies. 
117 
that the quartzites of Sutherland and their subordinate limestonea were of 
Lower Silurian age ; and was strengthened in the opinion, whicli 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 185G Colonel James and Prof. Nicol separately observed the unconfoi-mable 
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 Suthcrlandshire 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 Kmestones 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 quai-tz-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 SerpuUtes 
Maccullochii, and traces of fucoids. The.'ie fossils were long ago noticed, but of 
late they have been traced in beds for great distances by Mr. Peach. I'he 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 Macltirca Peachii, spec, 
nov. (and its curious twisted operculum), Ophilcta compacta, well known in Canada, 
Oncoceras, spec., and Orthsceras, 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 ia 
Kintail, on the west, to the frontier of the Old Red Sandstone on the cast, the 
general succession of rocks was described to be much the same as that in 
North-west Suthcrlandshire, though thcro arc considerable changes of lithological 
