Dr Nick Chidlaw is proposing to run the following
2 indoor courses in the autumn, if there is sufficient interest and availability of people to make the courses viable. The courses focus on exposures that are no longer extant / minerals that are rarely seen today in the area described. The courses would run on the same weekend, although independent of each other. They would be held at
The Chantry in Thornbury. They would comprise powerpoint-based lectures, together with examination of hand specimens of relevant mineral and rock types, and published geological maps. No prior knowledge of geology or the study areas is assumed.
THE FORMER WYE GLACIER FRONT AT HEREFORD
Saturday 27th October 10.00 am – 5.00 pm
Some 26,000 years ago, much of northern and western Britain lay below continuous glacier ice, and adjacent lands were occupied by inhospitable tundra. The Wye Valley Glacier, over 200 m thick, reached as far east as Hereford, where local hills protruded island-like above the ice sheet. This course offers an opportunity to study the legacy of a glacier, located some 40 miles from Bristol, from the most-recent cold climatic phase. Highlights include the plugging of the pre-glacial valley of the river causing its re-direction to that seen today, and the pond-studded kettle-kame moraine with its striking fold structures produced during melting of contained ice.
METAMORPHISM AND MINERALISATION IN THE BRISTOL – MENDIP AREA
Sunday 28th October 10.00 am – 5.00 pm
Following the end of the Carboniferous period around 300 million years ago, the area of the earth’s crust that became the British Isles began to stretch and heat as the North Atlantic Rift basin began to form. In the west of England, subsiding rift basins developed where the Cotswolds and Somerset Levels now lie. Between these places, in the Bristol – Mendip area, the crust was under tension at times, causing opening of lines of weakness including faults, joints and fissures. Into these created spaces, and cave systems, descending and ascending chemical-rich fluids accumulated, cooling and crystallizing to form mineral deposits. They include deposits of iron and manganese in Triassic times, and chiefly lead and zinc sulphides in Middle Jurassic times. Associated with the latter, other fluids spread extensively through porous strata in some areas, metamorphosing them to a silica-rich rock. Subsequently, many of these mineral deposits became of significant economic importance to man. This course will familiarise attendees with the history and character of this mineralization, and the impressive variety of mineral types that have been collected in the area in the past.
Tuition fee per course is £25.00 per person. The deadline for receipt of fees is 27th September. For further details of either or both courses, contact Nick Chidlaw.
1 comment:
It's not often there's a course on glaciation. The British ice sheet spread as far south as the M4, and the wind-blown dust from the dry desert edges of the glaciation formed loess deposits in the Wye valley and various sites along the Welsh coast and inland.
The Irish sea was frozen over too, and sea-levels were several hundred feet lower than today, so much water was locked up in the ice. Where Stockholm is, the ice was over a kilometre thick, the weight causing a significant depression in the crust. Several rivers changed their courses too, including the Bristol Avon, and the Ulster Bann which had to flow out through Belfast Lough, as Lough Neigh was blocked by ice to the north.
So it should be a fascinating course!
Ian Donaldson (WEGA)
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