344 ON THE RED SANDSTONE, MARBLE, 
much the greater part has been washed away by the waves and 
currents of unreckoned ages. But if this sandstone belong in 
reality to the Old Red system, what, I asked, are these appar- 
rently associated beds of stratified limestone and shale? Are 
they not the representatives, though mayhap in an aliered state, 
of those Old Red ichthyolitic beds which, overlying the great 
conglomerate, exist in Ross, Cromarty, and Moray, as alternat- 
ing layers of lime, clay, and sandstone, and occur in Caithness 
as the extensively developed flagstones so well known in com- 
merce as Caithness flag? And it was chiefly in the hope of 
finding some data on which to determine the true answer to the 
query that I last autumn visited Assynt. 
I had examined, in the previous year, the Old Red Sandstone 
of Ru-Store and Durness, and satisfied myself that it is the 
same rock which is developed in these localities that forms the 
insulated hills of Sulvein, Coul-beg, and Coul-more, and which 
occurs at Gairloch in Ross-shire, in the southern parts of Skye, 
and in the island of Rum; and further, that in Sutherland, as 
in Ross and Iverness-shires, it rests unconformably on a base 
of gneiss. I now fixed on Inch-na-damph, near the head of 
Loch Assynt, as the best possible centre for examining the 
associated deposits of the district. It lies within less than two 
hours’ walk of both the upper and lower beds of the great sys- 
tem to which all the upper rocks of Assynt belong, and is in 
the immediate neighborhood of a range of noble precipices, — 
the crags of Stronchrubie,— which present a magnificent sec- 
tion of the stratified limestone. Beginning with these, I traced 
them upwards from near their base to the deposit which rests 
over them (an immense bed of quartz rock, that forms by much 
the greater part of one of the loftiest of the Sutherlandshire 
hills, — Benmore) ; and then, reversing my course, traced them 
downwards, with the deposits which lie under them, until I 
reached the fundamental gneiss of the country. Without, how- 
