Harlaw is not only a beautiful Sunday walk but demonstrates a wide range of Lower Carboniferous sedimentary rocks including sandstones, mudstones and dolostones (cementstones). These sedimentary rocks provide information and aid an appreciation of the geography and environment around 355 million years ago. Sedimentary structures within the sandstones are particularly useful in understanding the Lower Carboniferous landscape. One such example is located on the eastern shore where the stream enters. A sample taken from this spot was analysed and found ancient fossilised plant spores that enabled accurate dating of the rock. The site offers peaceful walks through wooded areas, a local nature reserve and stunning views across the reservoir toward the Pentlands.