Chap. VIII.] GENEKAL EELATION, SCOTTISH HIGHLANDS. 
171 
the development of the formation of Lingula-flags fills up the interval 
which is marked by the break in the North-west of Scotland. The 
Durness fossils are of the Lower Llandeilo age, and indicate a zone 
younger than the Potsdam Sandstone of North America, which I regard as 
equivalent to the Lingula-flags of England, the Alum-slates of Scandinavia, 
or the ' Zone primordiale ' of Barrande. It is therefore a fair inference 
that in the North of Scotland the base of the Silurian system is represented 
by the lowest quartz-rock (c 1 of the preceding section, p. 169), which is 
seen to repose transgressively on the Cambrian rocks. 
In following these metamorphic strata from Sutherland along the west 
coast of Eoss-shire, in the years 1858, 1859, 1862, <fcc, I entertained no 
doubt that the crystalline limestones on the shores of Loch Keeshorn, Loch 
Carron, Loch Alsh, and Loch Duich, with the associated chlorite-schist, 
mica-schist, and quartz-rock, are of the same age as the lower quartz and 
limestone of Sutherland, like which they are also overlain by the rock 
mapped by M'Culloch as gneiss (c 3 of the section). To satisfy myself on this 
point, I traversed the lofty watershed which separates Kintail from Strath 
Glass, ascending from Inverinat through the striking pass the Bealloch of 
Kintail, to Loch Affric, and there found a vast thickness of regularly 
bedded gneissose, micaceous, and quartzose rocks, all of which have the 
same strike as the fossiliferous rocks of Sutherlandshire, and which, 
despite of undulations, have also a prevalent dip to the E.S.E. 
The foregoing long section (p. 169) shows the general relations of all these 
North- Scottish rocks, from the most ancient Laurentian gneiss, through the 
Cambrian and Lower Silurian to the summit of the Old Red Sandstone on 
the eastern coast *. In addition to this illustration, it is of primary im- 
portance, towards a full comprehension of this great branch of my subject, 
that the reader should also have before him a diagram, drawn by my asso- 
ciate Mr. Geikie after our joint examination of the Highland rocks in 
1862, which shows the extension of the metamorphosed Silurian strata 
of the Highlands by anticlinal and synclinal folds, and correlates them 
with their unaltered equivalents in the South of Scotland. Instead of 
presenting a mass of disorderly rocks from which no system could be 
evolved, the Scottish Highlands are found, on examination, to consist of 
mountains and valleys in which the same geological laws are followed as 
among those where the strata are in no way metamorphosed. Hence we 
* In the summer of 1859 I induced my friend the Laurentian Gneiss from the younger gneissose 
Professor Kamsay to accompany me to the West- rocks of the Highlands ; and, in consequence of 
ern Highlands to test the accuracy of the con- his opposition, 1 went with Mr. Geikie, in 1860, 
elusion at which I had arrived respecting the to reexplore the region in question. The long 
separation of the younger gneiss and mica-slate memoir we published (Quart. Journ. Geol. Soc. 
from the Fundamental Gneiss, by the interpola- vol. xvii. p. 171), with many diagrams, has, I trust, 
tion of fossiliferous Lower Silurian and Cambrian settled the dispute. Professor Harkness, after 
rocks. He not only supported me in my view, two surveys of the Highlands, had indeed ar- 
but assured me that the fundamental gneiss of rived at some of the same results. See Quart, 
my section must unquestionably be the equivalent Journ. Geol. Soc. vol. xvii. p. 256. This view was 
of the Laurentian system of Logan in British first placed on record by me in a Geological Map 
North America, a survey in which country he of the Highlands (Quart. Journ. Geol. Soc. vol. 
had just made under the guidance of Sir W. xv. p. 353) ; and subsequently it has been more 
Logan. Professor Mcol is the only geologist, as closely and accurately defined in the Geological 
far as I know, who has opposed the separation of Map of Scotland, by Mr. Geikie and myself (1862). 
