Area: 21.91 hectares.
Description and Reasons for Notification:
A Geological Conservation Review site.
This site provides a superb example of Cornubian coarse biotite granite of small megacryst type (S-type), within the Permo-Carboniferous Bodmin Moor intrusion. The granite has a strong, approximately north-south trending sub-vertical tectonic foliation, emphasised by orthoclase megacrysts and irregular bands of strained quartz. This site provides one of the strongest examples of this texture and unique, unambiguous evidence of a deformation origin. The deep quarries also clearly demonstrate that the sub-horizontal jointing within near-surface granite exposures disappears with depth, and are not therefore an original cooling feature. Other important features of this site include a major occurrence of fresh, fine-grained megacrystic biotite granite and three substantial outcrops of late-stage granite porphyry (‘elvan’) dykes.
All these features are of key importance in deciphering the complex intrusive history of the Cornubian batholith during the late Palaeozoic.