The abnormally large “hushes” of Teesdale, North Pennines, England: Differentiating mining legacy and natural landforms in glaciated Carboniferous bedrock terrain

Abstract

The unusually large, steep-sided gullies and gorges incised into bedrock at Coldberry Gutter and Pike Law in Teesdale in the North Pennines are traditionally associated with ‘hushing’, a hydraulic mining process designed to gain access to lead-bearing veins. However, it is difficult to reconcile the size and form of these features, as well as the bedrock geology, entirely with a hushing origin. Instead, it is proposed that these landforms originated naturally on valley sides and interfluves through a combination of karstification, spring sapping, steephead evolution, fluvial slope channel enlargement, landsliding and meltwater channel erosion, which preferentially developed in fault and mineralised zones. The practices of hushing and quarrying then targeted the natural bedrock exposures for the extraction of visible mineralised materials, which were small and locally workable orebodies that would likely have led the way to the discovery of much more substantial mineralised ground and then subsequent adit excavation in adjoining areas. Large numbers of leats and hushing dams were constructed above and around Coldberry Gutter and Pike Law and were used to enlarge some engineered trenches/gullies (hushes), but were mostly too small to account for the excavation of the substantial volumes of bedrock necessary to create the largest incisions. Volume calculations on the alluvium located at the base of the incisions, likely to contain all the waste rock from the hushing process, are also incompatible with the total sizes of the proposed excavations; additional rock waste contained in spoil tips are composed of material excavated directly from adits within the gulleys and gorges. It appears that engineered reservoirs and leats were employed mostly to clear out waste material, wash processed rock and contribute to hydro-power activities in the larger gullies and gorges. Some of the most intensive hushing activity is in the surficial (Late Pleistocene and Holocene) deposits laid down by glaciation and postglacial fluvial processes, suggesting that it was employed also as a placer mining technique.