The substance of the following paper was given at a meeting of the Geological Society of Edinburgh on January 20th this year. Its object is to show that the group of Lower Scottish Limestones about Dunbar and round the Midlothian Coalfield does not represent any part of the Mountain Limestone of Yorkshire, but is the equivalent of the upper part of the Yoredale Series of Phillips, while the Edge Coals and Upper Limestones of Midlothian represent a series of beds which in Yorkshire and Northumberland lie above the true Yoredale Series of Phillips, and which were included by him in the Millstone Grit. It necessarily follows from this correlation that the lower part of Phillips' Yoredale Series, together with the Scar or Mountain Limestone of Yorkshire, are represented in Scotland by the Calciferous Sandstone Series, which is mainly a fresh-water deposit.