The torridon mountains in Wester Ross are fairly unique in scotland. They are made of ancient Torridonian sandstone, one of the oldest rock in the country. It was formed c. 1200 to 850 million years ago on a base of even older Lewisian gneiss. On the summits (of Beinn Eighe anyway) there is frost shattered cambrian quartzite which makes for interesting scrambling.
Note the mountains look a little more impressive without the wideangle!