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Geology Autumn Newsletter - 2015

During the summer, we investigated reports of a granite outcrop within the Jersey Shale Formation at the Bellozanne Recycling Centre, in an area not normally accessible to the public.  Investigations showed that exposures of laminated shale (Jersey Shale Formation) and flow-banded andesite lavas (St. Saviour's Andesite Formation), rather than granite, were exposed.  It is probable that the two Formations are separated by a faulted boundary.  This is in contrast to the geological map which shows only the Jersey Shale Formation to be present at this locality.  This was followed by a trail among the various granites between the Seymour Refuge tower and La Rocque Harbour where we found large quartz enclaves and pebbles of a brown Fe sandstone, and pebbles of many different rock types not found on Jersey, some of which may have been used at La Cotte de Saint Brelade; outcrops of possible Ice Age mid-tide conglomerates were also found.  We also inspected a large 'outliner' of the Rozel Conglomerate and other erratics located in the gullies.

Lastly, we visited Le Pulec, an excellent site for exploring how the Jersey Shale was deposited, and examined the Shale-NW Granite contact with its adjacent veins of silver, lead, and zinc, and the Ice Age raised beaches, head and loess.

Our Autumn meetings are concentrating more on information gathering via illustrated talks and practical evenings in the Members' Room and at La Hougue Bie.  On 13th November there will be a talk entitled 'The Andesite Trail above the Shale' in the Members' Room at 8pm and on 27th Novemeber 'Cretaceous 2' also in the Members' Room at 8pm.  These and other talks can be found under Geology Section on our website.

During practical evenings at La Hougue Bie, we will cut and polish specimens of Jersey rocks for our data base but also samples of rocks and minerals collected during holidays.  Thin sections may also be made for the data base, while in the adjacent Library, collections of books and offprints (which may be borrowed) and sorted, recorded and filed for future study.

Copies of our field visits are available in fully illustrated booklets and in the Jersey Geology Trail book at the Société Jersiaise bookshop, along with the BGS Jersey Geology map and journal.  Descriptions of Jersey rocks and their history are also on the website at www.jerseygeologytrail.net together with links to our field visits and walks.

Colin Cheney - Chairman.

Ralph Nichols - Secretary.

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