Thurlestone Rock
The arch shaped rock formation standing offshore on its own reef is Thurlestone rock. or "thirled stone". The local village is named after the stone.
The surrounding geology has an interesting mix of features. The Permian red Breccio-conglomerates, with their characteristic pebbles/cobbles set in them, lie on the Lower Devonian Meadfoot Beds which are made up of slates of varying colours.
The rock itself is Breccio-conglomerate sat on the Meadfoot Beds and is known as a Permian Outlier.
The Permian Breccia was formed between 251-299 million years ago by 'flash floods' in hot desert conditions and its red colouration is a result of hydrated iron oxide from alkaline groundwater, which oxidised to form Haematite.
The Devonian Beds are made up of pale green (Meadfoot) slate, micaceous schists, purple (Dartmouth) siltstones, quartz and quartzite. These were formed between 359-416 million years ago when the area was a coastal plain with shallow seas.
There are also unconformities causing gaps between the layers of rock. These are caused by lack of sediment laid down between the Devonian and Permian rocks, giving a striking difference between the two. The Devonian rocks have a twisted and folded appearance. This is due to tremendous pressure in the ancient past, of tectonic plate collision. This is unlike the Permian rock which have not been subjected to the same pressures and just lay on top of the Devonian.
To log this Earthcache please answer the following questions and send via my profile.
Question 1
Go to N50 15.733 W003 51.548
The Breccio- Conglomerate cliff here is gradually being eroded by the forces of nature, a cave has already formed behind the cliff and cracks/faults have already appeared. Can you describe, and explain, what is likely to occur in the future and name the feature that is likely to form?
Question 2
Go to N50 15.751 W003 51.553
Laying in the Meadfoot Beds slate at this point is a large quartzite crystal. Estimate the size of the crystal in inches.
Question 3
Go to N50 15.758 W003 51.581
At this point The twisted and folded Meadfoot Beds are pointing at what angle? Is it: a) Horizontal b) Vertical c) at an angle of 45 degrees?
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