Posted by: paulgarner | May 17, 2011

A taste of Cornish geology

Yesterday my wife and I arrived home after a weekend in St Ives, Cornwall. St Ives is a wonderfully picturesque town, with a delightful harbour, clear blue seas and sandy beaches. Formerly dependent on fishing, it is now a haven for tourism and the arts. The town abounds in galleries and potteries, as well as some excellent eateries. During our stay we enjoyed good weather and this allowed us to spend some time walking, enjoying the scenery and – inevitably – taking in the geology.

The Cornish peninsula is composed largely of Devonian and Carboniferous sediments intruded by a large granite body that can be traced eastwards into Devon and westwards to the Scilly Isles. Evidences of catastrophism are everywhere, so it’s a great place for the flood geologist to visit. Here are a couple of highlights from our brief trip.

The photo to the right shows Gurnard’s Head, a narrow headland composed of slates (metamorphosed mudstones) and sheet-like igneous intrusives, capped by pillow lavas (basalts that were extruded underwater). A cupola of the Land’s End granite is exposed at Porthmeor Cove, just west of Gurnard’s Head. Unfortunately the tide was in and I wasn’t able to access the best exposures in the cove, but the photo to the left shows cross-cutting veins of the granite penetrating the surrounding metamorphosed sedimentary rocks. Some years ago I collected samples of the Land’s End granite from another locality for Andrew Snelling’s research on polonium radiohalos. If you want to see the results, take a look at Snelling (2005), especially his figures 5 and 6 (pp.122-123) in which the extraordinary abundance of radiohalos in the Land’s End granite is very evident.

Reference

Snelling A. A. 2005. Radiohalos in granites: evidence for accelerated nuclear decay. In: Vardiman L., Snelling A. A. and Chaffin E. F. (editors). Radioisotopes and the Age of the Earth: Results of a Young-Earth Creationist Research Initiative, Institute for Creation Research, El Cajon, California and Creation Research Society, Chino Valley, Arizona, pp.101-207.

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