498 
THE GEOLOGIST. 
glomeratic grit between the older gneiss (see memoir in Trans, of British Asso- 
ciation) and the quartz rocks, the extent of this interpolation had not been traced ; 
nor, again, owing to very stormy weather, had he been able to satisfy himself that 
this red conglomerate was, or was not, conformable to the overlying quai'tzites 
and limestones. Aware that his friend Colonel James, R.E., was about to visit 
Sutherland, Sir Roderick requested him to determine the point, and this was 
clearly and satisfactorily accomplished by Colonel James, who traced over a con- 
siderable area a discordance between the red and purple sandstones of the north- 
vest coast and the overlying crystalline rocks. Later in the same summer. Pro- 
fessor Nicol, revisiting Sutherland, extended similar physical phenomena from 
Cape Wrath down all the west coast of Lochalsh in Ross-shire, and published 
his results in the "Quarterly Journal of the Geological Society." So far, 
then, as the physical order was concerned, i.e. from the fundamental or older 
gneiss up through great mountains of purple and red conglomerate uncon- 
formable to the rocks both below and above, and a series of quartz rocks with 
limestones, covered by younger gneiss, no doubt remained. But Professor 
Nicol, doubting the value of the parallel the author had endeavoured to establish 
between the few and imperfect fossils of these lower limestones and those of 
Lower Silurian age, suggested that the quartzites and limestones might be the 
equivalent of the carboniferous system of the South of Scotland. Wholly dis- 
senting from that hypothesis, Sir Roderick urged Mr. Peach to avail himself of 
his first leisure moments to re-examine the fossil beds of Durness and Assynt, 
and the result was the discovery of so many forms of undoubted Lower Silurian 
characters (determined by Mr. Salter), that the question has been completely 
set at rest — there being now no less than nineteen or twenty species of Maclurea, 
Murchisonia, Ophileta, and Orthoceras, with an Orthis, &c., of which ten or 
eleven occur in the Lower Silurian rocks of North America. 
Having re-visited the region this summer, accompanied by Mr. Peach, and 
enjoying good weather. Sir Roderick was enabled to observe at many points the 
grand succession of rocks above indicated, and to confirm the view which he had 
laid before the Geological Society, of these true Lower Silurian rocks being sur- 
mounted by micaceous schists and flagstones often passing into a younger gneiss. 
But whilst the author is convinced that most of the crystalline and subcrystalline 
masses occupying the central and eastern parts of Sutherland and Ross are of 
younger age than the fossiliferous rocks of the North-Western Highlands, he 
admits that there may be tracts in that vast extent of country where the older 
or fundamental gneiss may be brought to light. 
The ascending order, however, on the west coast of the Highlands — i.e. from a 
fundamental gneiss, through great unconformable purple sandstones up into 
siliceous rocks and limestones with Lower Silurian fossils — is in perfect harmony 
with the general order in North America, worked out by Logan in Canada and 
by geologists of the United States, and confirmed at the recent visit of Professor 
Ramsay; for in that quarter of the world there exists a wide spread of ancient 
gneiss, which is termed Laurentian, surmounted by a series of stratified coarse 
rocks, termed Huronian ; and the last again is followed by sandstones and lime- 
stones, some of which, classed as Lower Silurian both by Logan in Canada and 
Hall in New York, contain the same fossils as the rocks of Sutherland. The 
intercalated purple and red sandstones (No. 2 of the Highland series) therefore 
clearly represent the Cambrian rocks, and are separated from the Old Red of the 
east coast by the whole series of the quartz rocks, limestones, micaceous and 
quartzose schists, all of which have afforded the materials out of which the true 
Old Red series has been formed. 
The second part of the communication related to the Old Red Sandstone, pro- 
perly so defined, as exhibited on the east coast, between the Orkney aad Shetland 
Islands on the north, and Banfi'shire and Morayshire on the south, various points 
of which the author visited last summer. In Caithness and the Orkney Lilands, 
accompanied by Mr. Peach, the author made various interesting additions to his 
former knowledge, particularly as derived from the researches of Mr. Robert 
Dick of Thurso. His belief was sustained that the ichthyolitic flagstones of 
