Geologist. Born at Traquair in the Scottish Borders, the son of the parish minister, Nicol was educated at the University of Edinburgh, where he was inspired by the lectures of Prof. Robert Jameson (1774 - 1854). He continued his education in Germany, at Berlin and Bonn.
He was appointed Assistant Secretary to the Geological Society of London (1847), the Professor of Geology at Queen's College, Cork (1849), and finally Professor of Natural History at the University of Aberdeen (1853), where he worked until his retirement in 1878.
Nicol began by examining the geology of the Tweed Valley and was the first to explain the succession of the fossiliferous Ordovician and Silurian rocks in this area. He was awarded prizes by the Highland Society for his work. In his paper 'On the Structure of the North-Western Highlands' (1861), Nicol understood the relative positions of the Torridonian sandstone and Durness limestone in Sutherland and how they were related to the nearby schists, whereby older rocks overlaid younger rocks brought about by what is now referred to as the Moine Thrust. Nichol's views contrasted with those of Sir Roderick Impey Murchison (1792 - 1871), whose reputation was such that his interpretation was accepted by the scientific establishment. It was not until the work of Charles Lapworth (1842 - 1920), which was confirmed in the field by Ben Peach (1842 - 1926) and John Horne (1848 - 1928), that the value of Nicol's work became clear. However, in 1869, Nicol was to incorrectly interpret the Parallel Roads of Glen Roy as being of marine origin.
He was elected Fellow of the Royal Society of Edinburgh in 1847.
Nicol died in London, but was buried in Grange Cemetery in Edinburgh.
