
OLD RED SANDSTONE OF WESTERN EUROPE. 383 
I was informed, indeed, by Mr Crawrorp, Tongue House, that on Beiun 
Armuinn, a mountain, rising to a height of 2338 feet, in the heart of eastern 
Sutherlandshire, conglomerate occurs. 
The extreme north-western limit to which the Old Red Sandstone can now 
be traced may be drawn at the Kyle of Tongue. Detached ridges and knolls 
referred to this formation were observed there by SEpGwick and MurRcHISON 
in 1827.* They were described in further detail, and inserted on his map by 
Hay Cunnincuam, in his “ Geognostical Account of Sutherlandshire.”+ But 
by much the most extensive and instructive series of sections of these deposits 
occurs, not on the mainland, but on the Roan Islands, at the mouth of the Kyle 
of Tongue, though there they do not show their junction with the crystalline 
rocks, as they are surrounded by the sea. These islands consist entirely of con- 
glomerate, a coarse well-bedded rock, with nests and partings of dull red sand- 
stone. The strata vary from less than a foot to several yards in thickness, and 
are marked off chiefly by these intercalated ribs of sandstone, for in the mass 
of the conglomerate itself the pebbles very commonly show no trace of strati- 
fied arrangement. The bedded character of the rock, however, comes out very 
clearly even from a distance, the successive ledges shelving down into the water, 
and dipping out to sea at angles of 10° to 20°. By means of the joints, slices 
have been cut away from the cliffs, leaving vertical walls against which 
the Atlantic surge is always heaving. These precipices are deeply fissured by 
the opening of the joints, whereby the waves have been able to perforate 
the rock in many gullies and caves. On the north side, where the beds 
slope like a long breakwater into the sea, huge masses of the conglomerate have 
been loosened and moved down the inclined surface of the beds below them. 
But the most ruinous scene is presented by the south-western or inland face of 
the larger island. Owing to the abundant joints and the more decomposing 
nature of the rock at that place, the ground seems caverned and honeycombed 
in all directions.{ At the north end of the smaller island, in Meal Chalam and 
the neighbouring headlands, the rock assumes its noblest forms, rising into 
massive buttressed sea-cliffs, a fitting termination for the Old Red Sandstone 
in the north-west of Scotland. 
The component pebbles of the conglomerate vary in size up to one foot or 
rather more in length. They are mostly rounded in shape, but include sub- 
angular stones, particularly where the material happens to be of a jointed 
* “Trans. Geol. Soc.,” 2d series, vol. iii. p. 127. 
t “Trans. Highland Society,” vol. vii. 
} The tradition, so commonly told in such districts, is repeated here, of a dog having fallen into 
one of the subterranean passages, and having worked its way underground until, after some days, it suc- 
ceeded in crawling out at an opening on the opposite side, but devoid of its hair, which had been 
Seraped or shaved off by the rough walls of the narrow passages through which it had to force its 
way ! 
