Folly Rocks
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Condition (Natural England)
| Unit | Feature | Condition | Area (ha) | Assessed |
|---|---|---|---|---|
| SW573280 | — | Favourable | 2.51 | 2010-01-29 |
Geology & landscape
Geological Period: Permian · Rock Type: Granite
Landscape processes: Volcanic / Igneous
Description
Folly Rocks SSSI Description This site shows a granite porphyry (‘elvan’) dyke, some 18 metres wide, unusual for its readily discernible multiple character. Three distinct, fine-grained, acidic rock-types are interpreted as representing two successive injections involving a combination of liquid, crystal and gaseous phases, as distinct from simple fluid magmatic emplacement. Internal features such as chilled margins, flow banding and xenolithic and xenocrystic fragments are well displayed. The dyke is the best example of the ‘elvan’ suite of south-west England. The suite is approximately 20 million years younger than the granites and represents the culmination of acid magmatism in south-west England during the Permian period.