In the wider catchment the geology is more varied, ranging from the Precambrian rocks of the Charnwood Forest, through to the Jurassic limestone that forms the Lincolnshire Edge and the eastern watershed of the Trent. The most important in terms of the river are the extensive sandstone and limestone aquifers that underlie many of the tributary catchments. These include the Sherwood sandstones that occur beneath much of eastern Nottinghamshire, the Permian Lower Magnesian limestone and the carboniferous limestone in Derbyshire. Not only do these provide baseflows to the major tributaries, the groundwater is an important source for public water supply.