Area: 5.80 hectares.
This is a new Geological Conservation Review site.
The site at Ashburton Road Cuttings is represented by the approximately 1,500 metre long exposure located along the south-western side of the A38(T), on the southern part of the Ashburton by-pass.
At this site a melange sequence of probable Frasnian (Upper Devonian) age is seen overlying the Famennian (Upper Devonian) Kate Brook Slate Formation. The boundary between the two formations is the Bickington Thrust --a major tectonic boundary which separates the younger formations from the Frasnian and older sequences to the south in this part of Devon. This site includes the most instructive and easily accessible exposures of the Bickington Thrust and adjacent sequences. This major boundary is not exposed on any coast. The melange sequence consists of shallow water limestones of 'reef' facies, and volcanic rocks set in a grey slate matrix. The limestones and volcanics form clasts up to tens of metres in length. It is uncertain whether the melange is tectonic or sedimentary in origin. This chaotic facies passes upwards into the Gurrington Slate, with volcanic lenses and rare dolerite intrusions exposed toward the southern end of the cutting.