massif. Ruadh-stac Beag (), which lies on a spur from the main ridge east of Ruadh-stac Mòr, has sufficient relative height to be classified as a Corbett. One of the most famous features of Beinn Eighe is the corrie of Coire Mhic Fhearchair, often simply known as the "Triple Buttress Corrie" after the three large rock features which dominate the view from the north. There are many rock climbs on the buttresses and hillwalkers can access the tops of the buttresses from the head of the corrie. Geology In common with much of the Northwest Highlands, the underlying rocks of the area are composed of Lewisian gneiss, a very ancient rock type. The younger Precambrian Torridonian Sandstone, which sits on top of the gneiss, forms the bulk of all of the Torridon Hills, including Beinn Eighe, and was formed around 800 million years ago from the sediment of rivers that flowed across the landscape of the gneiss. Beinn Eighe is however unusual amongst the Torridon Hills in that the summit ridge is composed of white-coloured Cambrian basal quartzite. This is a very hard but brittle rock, that was laid down around 540 million years ago as pure white sands during a period when the area was flooded by warm tropical seas. The quartzite gives Beinn Eighe its familiar light coloured summits, which form a notable contrast to the other peaks in the area, and can appear similar to a covering of snow on the mountain. Within the Cambrian rocks a distinct rock layer, known as the Fucoid Beds, has been identified. The fossils found in the Fucoid Beds are very different to those from rocks of a similar age found in England, a fact that was crucial in establishing that during the Cambrian period the two land masses were separated by ocean. These fossils, which include trilobites, and worm burrows, are some of the oldest fossils to be found in Scotland. The fossil of one creature identified in the rocks of Beinn Eighe, Olenellus armatus, has not been found at any other location. The area was heavily sculpted by glaciers during successive ice ages. Flora and fauna Many rare plants, including two variants of dwarf shrub heath and a western variant of moss heath, are to be found at Beinn Eighe. In total 680 different species of plants have been identified, including the greatest variety of oceanic mosses and liverworts