The well-known northward attenuation of the massive Carboniferous Limestone of Lancashire and Yorkshire, and the gradual replacement of its thick calcareous groups by sandstones, shales, and seams of coal, with interstratifications of marine limestone, can be advantageously studied in the southern counties of Scotland. In these districts a characteristic and recognisable base for the Carboniferous system is presented by the deep red Sandstones and marles of the Upper Old Red Sandstone, which pass up conformably into that system, but rest with a violent unconformability upon every formation older than themselves, including even the Lower Old Red Sandstone of Berwickshire and the Cheviot Hills.