The Carboniferous sequence in the Westmorland Dales contains two internationally important sections, where the boundaries between various subdivisions (known as substages) of the Carboniferous Period have been defined. These sections, known as ‘stratotypes’, are of great significance to geologists researching the Carboniferous.
One section, in a crag above Potts Valley, contains the boundary between the Holkerian and Asbian substages of the Carboniferous. The Asbian substage was even named after this area. Another reference section, in the River Eden at Janny Wood in Mallerstang, contains the boundary between the Asbian and Brigantian substages of the Carboniferous. The research at these locations is based on detailed changes in the nature of the limestone and its fossils, including microfossils, and there is little obvious to see in the field.