River Wharfe - Geology

Geology

Upper Wharfedale is an area from the Lower Carboniferous era and lies north-west of Burnsall. Its main features are the Great Scar Limestone which forms a base to the overlying Yoredale Beds, a 300-metre deep strata of hard limestones, sandstones and shale. These have been slightly tilted, toward the east. To the south-east of the area are the Millstone Grit laid down in the Upper Carboniferous era, and is covered by heather moorland, hard crags and tors.

Weathering of the Yoredale Beds has produced a stepped profile to the valley sides, consisting of a shelf of limestone, sometimes grassy but often displaying such karst features as limestone pavement, gorges and sinkholes. During the last ice age, the local ice cap at the head of the Dales fed glaciers to produce the classic U-shaped profiles seen today.

Where the river valley changes course into Lower Wharfedale, the change of underlying rock can be seen in the darker stone in the field walls. The Millstone Grit outcrops at the Cow and Calf Rocks near Ilkley form a rolling dissected plateau. Due to the impermeable nature of the rock, blanket bogs and mires form, and drier areas have wet and dry heaths and acid grasslands.

Coarse sandstones in the area are known as Addingham Edge and Bramhope Grits. The Otley Shell Beds become exposed at Otley Chevin. At Great Dib Wood the Otley Shell Bed is sandwiched between two Namurian sandstones.

Glacial lakes once filled Lower Wharfedale and deposited sand and gravel. These were quarried and now form the basis of the Otley Wetland Reserve, and Ben Rhydding and Knotford Nook gravel pits.