Prof. C. Lapworth—The Secret of the Highlands. 125 
area of this character, let us first examine the corresponding strata, 
as shown in the parallel valley of Loch Eriboll, where, if the visible 
phenomena are reliable, we again find an unmetamorphosed limestone 
and quartzite series, lying between the two generally metamorphic 
formations of the Hebridian gneiss and the Sutherland Series. 
1V.—Appearances in the Loch Eriboll Area. 
The long and narrow valley of Loch Hriboll lies a few miles to 
the eastward of the Strath of Durness, from which it is separated by 
the steep mountain ridge of Ben Spionna and Ben Cannabin. The 
northern and central parts of the valley are filled by the waters of 
the beautiful sea-fiord of Loch Eriboll, which is about ten miles in 
length, by two in breadth. The southern extremity of the valley is 
formed by the marshy flat of Strath Beag, which is shut in on all 
sides, except to the north, by the converging heights of Craig Hrail 
and Conamheall. 
The western wall of the valley of Loch Eriboll—the range ot 
Ben Spionna and Ben Cannabin (25387 ft.)—is composed of the 
almost vertical Hebridian gneiss, overlain by sheets of the Lower 
Quartzite, which dip gently eastward and finally subside below 
the waters of the loch. Some islands in the loch itself, and the 
promontories along its eastern shore, are formed of thick-bedded 
limestones. These, like the underlying quartzites of Ben Spionna, 
dip generally at gentle angles to the eastward towards the mountain 
ridge of Ben Poll and Whiten Head, which forms the eastern wall 
of the valley, and constitutes the most westerly buttress of the great 
plateau of Central Sutherland. In the lower parts of this ridge 
the limestones appear to be generally surmounted by a second 
series of quartzites and flaggy beds (Upper Quartzite of Murchison 
and others). In its higher slopes this Upper Quartzite plunges in 
its turn below the flaccy schists, metamorphic gneisses and so-called 
igneous rocks, that make up the Upper or Flaggy Gneiss Series of 
Central Sutherland and the Highlands generally. 
V.—Sections West of Loch Eriboll. 
In my study of this area J ascertained that upon the western side 
of the Loch, the Lower Quartzite rests unconformably upon the 
Hebridian gneiss of Ben Cannabin. 
I. a. The basal zone (a) of this lower quartzite is a well-marked 
breccia, or conglomerate, rarely more than a foot or two in thickness, 
filled with small quartz pebbles, angular fragments of vein quartz, 
and flakes of grey and greenish shales. 
The main mass of the Quartzite itself is divisible into two primary 
ZONES, VIZ :— 
I. b. A lower zone, of thick-bedded and occasionally flagen 
quartzites usually weathering to a faint pink or buff colour. (Tinted 
Quartzite. ) 
I. c. A higher zone of massive quartzites, usually of a pure white. 
(White Quartzite. ) 
I. d. The highest zone, as in Durness, is composed of flage 
