During the construction of the Settle-Carlisle Railway, shale was extracted from the exposed rock faces on either side of - and below - the lower waterfall at Force Gill, significantly widening the otherwise narrow, naturally 'V'-shaped valley at this point.
As there was (is) no naturally occurring sand or gravel in this area, the shale was ground-up then either mixed with clay to make bricks or mixed with ground-up gritstone and burnt lime to make mortar / concrete. These essential building materials were then used to construct the bridges (including Ribblehead Viaduct) and other key structures along the Ribblehead - Blea Moor section of the line.