PlyMouth International - The Plym Valley Trail is quite a gentle route for both cyclists and walkers heading out from Plymouth towards Dartmoor. Passing through Plym Bridge Woods, managed by the National Trust, the trail offers great views and the opportunity to get close to wildlife, as well as being of interest to the geologist.
In particular, the disused sites of Cann and Bickleigh Vale quarries are worth a look. Both quarries were used to mine slate, with Cann Quarry being worked as far back as 1683. The slate was used in roofing and flooring, though regrettably it was markedly inferior to the Welsh product.
The slate was originally a marine mud which, having been buried and turned into mudstone, was heated and compressed as a result of the tremendous forces at work during a collision of tectonic plates. This process altered the orientation of the minerals within the mudstone allowing it to split easily. That is, it had become slate.
Both quarries are cut by a fine grained granite dyke (molten rock which intrudes into the local rocks). This feature is actually known as an elvan dyke, ‘elvan’ being an old south-west mining term for granite dykes.
During the breeding season Cann Quarry is home to a pair of peregrine falcons and there is usually a viewing station with telescopes available for use. (inhilterkini.com)
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