170 
SILURIA. 
[Chap. VIII. 
of the mountains represented in the following vignette, and the commence- 
ment of the deposit of those sandy and calcareous beds, since converted 
into quartz and marble layers, in which the Lower Silurian fossils were 
entombed (c 1 & c 2 of the section, p. 169). 
It followed, therefore, that the subjacent red sandstone and conglome- 
rate, b, reposing upon the most ancient gneiss of Britain, are to be con- 
sidered of the same date as the similarly constituted purplish-red and 
pebbly sandstones of the Longmynd, which, in the typical region of 
Shropshire, underlie all the Silurian strata (p. 24). There, however, as 
well as around Harlech in North Wales, these Cambrian rocks graduate 
upwards into the superjacent Silurian rocks; and the period occupied in 
Canisp. Suilvein. Coulmore. 
Mountains on the West Coast op Sutherland and Ross. 
The above pictorial view, from a sketch in my possession taken by that accomplished 
Highland chieftainess the late Duchess Countess of Sutherland, represents the three 
isolated mountains of Canisp, Suilvein, and Coulmore. The strata of red sandstone 
and conglomerate (now known to be Cambrian, b of the preceding section) may be di- 
stinguished by the horizontal lines marking the stratification. The lower buttresses of 
the mountains are composed of the ancient gneiss with granite veins (a of the section). 
Hugh Miller's description of these great masses of red and chocolate-coloured con- 
glomerate and hard sandstone, which are seen reposing upon the oldest gneiss of Scot- 
land, and which, as above explained, are overlain in their range to the north by the 
Lower Silurian quartz-rocks and limestones of Assynt and Durness, is so eloquent and 
so true that I gladly cite a portion of it. " Rising over a basement of rugged gneiss 
hills, that present the appearance of a dark tumbling sea, we descry a line of stupendous 
pyramids from 2000 to 3000 feet in height, which, though several miles distant in the 
background, dwarf, by their great size, the nearer eminences into the mere protube- 
rances of an uneven plain. Their mural character has the effect of adding to their 
apparent magnitude. Almost devoid of vegetation, we see them barred by the lines of 
the nearly horizontal strata, as edifices of man's erection are barred by their courses of 
dressed stone ; and while some of their number, such as the peaked hill of Suilvein, 
rise at an angle at least as steep and nearly as regular as that of an Egyptian pyramid, 
in height and bulk they surpass the highest Egyptian pyramid many times. Their 
colour, too, lends to the illusion. Of a deep red hue, which, in the light of the setting 
sun, brightens into a glowing purple, they contrast as strongly with the cold grey tone 
of the gneiss tract beneath, as a warm-coloured building contrasts with the earth-tinted 
street or roadway over which it rises." 
