The Ten Fathom Grit of the Millstone Grit Group is the most continuous sandstone that can be mapped, however, it does not always comprise thick sandstone beds, but may include micaceous and thinly-laminated sandstones that have been quarried at various sites in Upper Swaledale for roofing slates. It can be difficult to differentiate many of the Millstone Grit sandstones as they commonly have the same grey coloration with orange, iron staining. The buildings of Keld in Upper Swaledale were all constructed using sandstone from Ten Fathom Grit.
The Upper Carboniferous Millstone Grit Group is interpreted as a large fluvio-deltaic sequence of mudstones, siltstone and coarse-grained pebbly sandstones. Although the depositional paleoenvironment was supplied with sediment delivered from a range of provenances, the dominant supply was from eroded remnants of Scottish and Norwegian Caledonian Mountains located ~450 and ~950km towards the north and north-east, respectively. Some thin coals up to ~1 m thick occur at Tanhill. These coals were worked from the thirteenth century until the early 1930s on the moors near Tan Hill and helped to fuel the lead smelting mills.