Torridonian sandstone

In geology, the term Torridonian is the informal name for the Torridonian Supergroup, a series of Mesoproterozoic to Neoproterozoic arenaceous and argillaceous sedimentary rocks, which occur extensively in the Northwest Highlands of Scotland. The strata of the Torridonian Supergroup are particularly well exposed in the district of upper Loch Torridon, a circumstance which suggested the name Torridon Sandstone, first applied to these rocks by James Nicol. Stratigraphically, they lie unconformably on gneisses of the Lewisian complex and their outcrop extent is restricted to the Hebridean Terrane.

The rocks are mainly red and brown sandstones, arkoses and shales with coarse conglomerates locally at the base. Some of the materials of these rocks were derived from the underlying Lewisian gneiss, upon the uneven surface of which they rest, but the bulk of the material was obtained from rocks that are nowhere now exposed. Upon this ancient denuded land surface the Torridonian strata rest horizontally or with gentle inclination. Some of the peaks, such as Beinn Eighe, are capped with white Cambrian quartzite, giving them a distinctive appearance when seen from afar. Some of the quartzite contains fossilized worm burrows and is known as pipe rock. It is circa 500 million years old. The Torridon landscape is itself highly denuded by glacial and alluvial action, and represents the remnants of an ancient peneplain.

...
Wikipedia