Structural Highs & Lows
The main structural components of this region are the Askrigg Block (Hudson 1938) and the Craven Basin (Hudson 1933). The elevated position of the Askrigg Block is caused by the underlying Wensleydale granite previously discovered by the British Geological Society by sinking a borehole (Raydale). The Craven Faults therefore play an important part in depicting exactly where the junctions between 'block & basin' occur.
Sink Holes - evidence for the North Craven Fault Unlike the South Craven Fault with its Great Scar Limestone and Millstone Grit on either side of the main Settle Ingleton trunk road, evidence for the North Craven Fault can only be noted by the sink holes that run adjacent to Mastilles Lane. The photograph above shows the line of the these sink holes. Like the South Craven Fault, the North Craven Fault continued to be active well into post-Triassic times.
Shatter Zone As you follow the line of the sink holes towards the top end of Gordale notice that the limestone outcrop has a somewhat shattered appearance. Once again this is evidence for the line taken by the North Craven Fault.
Mineralisation is commonly associated with the Craven Fault Zone. Pikedaw (SD 881638) is the location of a Calamine Mine: well worth a visit whilst in Malham. Other minerals found include baryte, sphalerite and azurite.
Silurian Basement Beyond the fault zone ( a slightly to the left) you will come across a depression as shown in the photograph. We have to thank glaciers for scouring out enough Carboniferous limestone to reveal the rocks - the same rocks that lie below Malham Tarn.
These rocks are Silurian (Ludlow) in age and are known as the Horton Formation. They are described as laminated hemipelagic silty mudstones.