Humberside Geologist no. 10

Members' Evening 1992

The Members' Evening was held on 16th January at the Grammar School Museum in Hull. The meeting was attended by 29 members and guests and consisted of a programme of lectures and displays.

Our President, Terry Rockett, was the first speaker, and he presented a lecture about Extinction Events in the Fossil Record. He pointed out that usually when people think of extinctions they immediately think of the Dinosaurs. But that is not the only extinction event to have occurred and it was by no means the worst.There have been events in most of the Geological Periods, often followed by bursts of rapid evolution amongst surviving groups. Terry suggested that the extinctions were largely due to anoxic or cold bottom waters flooding onto the continental shelves. The worst event was in the Permian, when 95% of all species and 50% of marine families died out. At the end of his talk Terry posed the question of whether we are now living during an extinction event and perhaps causing it?

Ron Harrison was the next speaker and he presented a stratigraphical column of the building stones used in Hull and the surrounding areas. Rocks of most periods can be seen, from the "Baltic Brown" granite from Finland, which is used as a decorative stone on shop fronts, to the use of local Quaternary Boulder Clay for making bricks. He also reminded us that mineral deposits were the original source of the copper, lead, glass and aluminium used in buildings. Ron showed slides of some of these rocks and bricks, and also included a photograph of a cottage built from boulders. He said that he had wondered where the boulders had come from, but had found the source and photographed it for us they were being carefully cultivated in a neighbouring farmer's field!

During the interval, when coffee was kindly provided by the Museum. Felix Whitham gave a short description of the techniques he uses to extract and clean the fossils in his award winning collection. He showed how he used a home made vice to grip specimens whilst he carefully removes the matrix using masonry nails. He also described how he recently used a bow saw to cut a large Inoceramus from a block of Chalk and he explained the secret of his much admired display specimens - he polished them with Kiwi brand boot polish.

Members had the chance to look at specimens on display from the collections of David Hill, Mike Horne, Gordon Lockwood, Roy and Beryl Osborn and Felix Whitham.There was also a display of recent acquisitions by Hull Museums.

After the break, three members of the Society described a geological tour in Southern France with the Hull University Adult Education Department. Clare Heyes told us that the study tour was based around the town of Lodeve, just north west of Montpelier and was led by Tony Benfield and Sheila Rogers.

The first section of the talk dealt with the features produced by erosion of the Jurassic limestone, which is extensive in this area, particularly to the north of the Permian basin in which Lodeve lies. The first feature described was the limestone gorge cut by the river Vis, which disappears north of Vissec to flow underground to its resurgence at Source De La Foux. This was visited after first viewing a cut off meander lower down river, at the Cirque De Navacelles.

Next the spectacular stalactites, stalagmites and crystal growths of the Grotte De Clamouse were illustrated. Followed by a description and illustration of the karstic landscapes found firstly at Les Rives, which on occasion is the site of a temporary lake and also at the Cirque de Moureze where dramatically eroded dolomitic limestone pillars form a 'ruin like landscape'.

Following Clare's photographs of the Karst scenery, Donald Beveridge showed a map of the mineral deposits in the area and drew attention to the proximity of the town of Bedereux, only 15 km to the west. A three dimensional section reproduced from a French geology book showed that, bounded by a fault, the dolomitic limestone of Moureze extended beyond Bedereux. A series of sketches was then shown demonstrating the deposition of bauxite in hollows in the limestone, due to chemical weathering in the Cretaceous period, this was subsequently covered by later deposits. Tropical weathering conditions and a high water table were necessary for this type of weathering. Bauxite is now quarried near Bedereux and photographs graphically illustrated a section of infill in the eroded limestone surface. Iron Oxide staining has coloured the bauxite red.

A second series of sketches illustrated the effect on topography of continuing erosion in the vicinity of volcanic intrusions. The baslaltic plug of the volcano's neck and 'filons' (dykes) are exposed, forming very significant features in the landscape. Photographs of such an exposure on the shore of Lac Salagou were shown illustrating a volcanic neck of Quaternary age standing above the Permian mudstones. Columnar jointing in the basalt plug could be seen. Photographs of the dyke showed it to be in places standing 3 metres high and 75 cm thick, with right angled changes in direction. A closed up showed vesicles in the basalt.

At this point the show cane to an abrupt end as the epidioscope bulb exploded! Mavis May was not able to present her part of the talk illustrating what really went on! She would have told tales of wine tastings, visits to the Roquefort cheese caves, nude bathing in the Mediterranean, gate-crashing a wedding party of the local gendarmerie and a lot more (with photographs to prove it)!

As well as losing the use of the epidioscope the meeting had run out of time so the Secretary hurriedly proposed a vote of thanks to the speakers, the exhibitors and the Museum, whilst members started to pack the exhibits away. Written by Donald Beveridge, Claire Heyes, Mike Horne and Mavis May.

From Humberside Geologist No. 10, 1992


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