Articles from Issue Number 11/5 October 2004

Charing Pit and Loose Valley
Led By Gareth George
17th September 2004

Early on Saturday morning a combined group of enthusiasts from OUGS London Branch and the Kent Geologists Group met our leader Gareth George, an old friend of London Branch, for a day of study in the Cretaceous Lower Greensand of the Western Weald.

Our first location was in the Folkstone Formation at Charing Sandpit in Hook Lane (TQ 935 493). This visit had been arranged with the kind co-operation of the owners Brett Aggregates. Operations in the pit had been suspended for the day and the Deputy Manager Steve Murrell and some of the staff accompanied us throughout the visit.

The faces exposed in the pit exhibited well developed cross stratified sets up to 2m. high consisting of moderately well sorted fine to medium yellow quartz sand. Closer investigation revealed variations in the direction and form of the foresets, some being asymptotic with dip angles reducing with depth and some more wedge shaped. Some reactivation surfaces could be seen, and considerable secondary iron staining (Leisegang rings). Gareth explained that these features are typical of sands deposited below the wave base in shallow shelf seas under the influence of strong tidal currents with well defined spring and neap cycles. The direction of dip of the foresets is produced by the dominant current, with the subordinate current forming reactivation surfaces. Gareth demonstrated that sequences of 28 to 30 foresets (tidal bundle sequences) could be recognised, the spring bundles being thicker than the neap bundles which tend to be more asymptotic . Each sequence may be terminated with clay drapes and/or reactivation surfaces Measurements of the direction of dip of the foresets indicated a current direction from the north-east, and Gareth explained that this conforms to the paleogeography of the area with a connection to the proto North Sea to the east of the high ground of the London Platform to the north. In marked contrast current directions in the Folkstone Formation in the Eastern Weald trend towards the Bedfordshire Straights in the north-west.

Further close investigation of the sands revealed that the dominant current sometimes changed direction, the two sets often separated by a highly bioturbated erosion surface. Many trace fossils could be identified, vertical Skolithos and Ophiomorpha burrows and large horizontal and sub-horizontal Thalassinoides. Some small scale climbing cross ripple laminations could be seen superimposed on some of the foresets, thought to be caused by vortices set up in the lee of the dunes.

In places the secondary iron forms hard concretions (carstone) which appear to be unrelated to bedding features or grain size, some even forming tubular structures. Similar features are seen in the Folkstone Formation throughout the Weald, and no simple explanation for their formation seems to be available. At the end of our visit Steve Murrell took us on a tour of the production facilities in the works. The pit produces some ¼ million tons per year of mortar sand to the building industry and retail outlets, and at the present rate of production the pit has a remaining life of about 8 years. The sand is first dumped through a coarse 150mm. screen to remove concretionary iron, then taken by conveyor to the fine screening plant where it is put through a 5mm. screen of parallel piano wires. Throughout the process the moisture content is closely controlled to produce to final moisture content of about 7%.

Lunch was taken at the Chequers Inn in Loose village, an excellent hostelry which serves Harvey’s Bitter!

Our second location of the day was a short walk from the Chequers via Salts Lane and a public footpath to the abandoned Kentish Ragstone quarry in Quarry Wood. On the way to the quarry we could see large blocks of the stone in use in the viaduct built by Thomas Telford in 1830.

Although the quarry is somewhat overgrown some excellent exposures are accessible, and show the typical alternating bands of ’Rag and Hassock’ typical of the Hythe Formation in this area. The Ragstone bands consist of hard massive sandy limestone up to 1m. thick, highly bioturbated and with sharp ero- (Continued from page 1) sional bases. The Hassock bands are generally thinner, and consist of loosely cemented glauconitic sands with occasional hard siliceous bands and low angle cross stratification. Some typical marine fossils were recovered. The fauna of the Hythe beds in this area is very varied, and includes ammonites, bivalves, belemnites, brachiopods and echinoids. The Hythe formation in this area is markedly different to that in the Western Weald, where it consists of heavily bioturbated glauconitic sandstones with lenticular chert beds and very rare fossils. There was some discussion regarding the cause of the alternating bands here, and the fashionable Milankovitch Cycles were invoked at one point. But why only in the Eastern Weald? Some faulting and large in-filled open fissures were seen. The fissures are known as ’gulls’, and are a feature of valley cambering. The competent strata are moving down-slope into the adjoining valley, sliding taking place over the underlying Atherfield Clay. So we came to the end of another excellent day.

Many thanks must go to Gareth for his enthusiastic and informative leadership, to Brett Aggregates for their kind co-operation, to Diana Franks of Kent Geologist’s Group for her liaison with Brett Aggregates, and to our own Di Clements for organizing the trip.

Brian Harvey

Building Stones of Westminster
Led By Eric Robinson
20th February 2004

Those of you who were lucky enough to attend the OUGS Symposium at Canford School this year might also have read that the architect Sir Charles Barry designed the wonderful Victorian buildings of the Tower, the Great Hall and the north front of the school. He was also the architect of the Houses of Parliament. For me this was a reminder that I had promised to write up the building stones walk that Eric Robinson led to Westminster, way back in February. So here, rather belatedly, are my memories of that visit.

Diana Wrench has already written about our visit to Westminster Abbey in the morning (See the April edition of the London Platform).

It was still bitterly cold after lunch when we met up with Eric again outside the front entrance to the Abbey and made our way round to the Houses of Parliament. There were other items of interest to see on the way.

First there was the Queen Elizabeth II 2002 Jubilee sundial made of concentric circles of varied stones lain flat in the pavement. The types of stone were, moving out from the inner ring around the central disc: Trevor microgranite from North Wales; Borrowdale tuff; red granite and Cornish granite. Two footprints have been placed where the observer should stand so that his or her shadow will fall on a scale that can be used to tell the time, but there was only diffused light on that grey and wintry day, with no sharp shadows.

Next we piled into a tiny shop in the Jewel Tower, where we bought cups of coffee to warm ourselves. The Jewel Tower was built by Edward III to store his clothes and jewels. It formed part of the original Palace of Westminster and survived the fire that destroyed almost all of the palace in 1834.

From there we went on to our main destination, the Palace of Westminster as it is today, otherwise known as the Houses of Parliament. It is built in dark yellow magnesian limestone. This choice of stone has been much criticised on aesthetic grounds, but it was actually rather a good one, because it is more resistant to weathering by London smog and acid rain than other limestones and has kept the detail of the carving crisp and undamaged.

Barry had been impressed by Southall Minster, which had previously been made in the same stone. It was quarried in Northern England and transported by barge via the Humber. On the small scale there are tiny gaps in the fabric, which were formed during diagenesis as a result of the transformation of CaO2 to MgO2.

Barry also made a sound choice of stone for the more rounded plinth, a Jurassic oolitic limestone from Lincolnshire. We could still see stone tool marks made by steel combs to remove any loose bits. We entered the building at the House of Lords end, furthest from Big Ben, and were shown into an entrance lobby where the elaborately decorative stonework included brocatelle, a Spanish marble from the Tertiary, Connemara marble from the Dalradian, black Valentian volcanic slate from the Silurian and red Monsal Dale limestone from Derbyshire. However, this was where the official guide took over from Eric. I won’t describe the rest of our visit in very great detail because I heard no more about the building stones and took no notes.

The famous architect Augustus Welby Pugin was only 28 years old when Barry enlisted his help to design the interiors of the building in1854, because of his knowledge of the Gothic style that had become extremely popular again in Victorian times. The next room we entered was a huge light and colourful hall used as a changing room by the Queen on her visits when opening Parliament. The decorative splendour was amazing, but was surpassed by the adjacent House of Lords with its elaborate golden throne and luxurious red leather seats. History oozed out of every nook and cranny of the place.

We walked on through the pivotal Central Lobby and the Members’ Lobby to the House of Commons, which was a lot more sober and subdued in its style and green colouration but still elegant and atmospheric. This chamber was destroyed in an air attack in 1941 and was redesigned by Sir Giles Gilbert Scott. It was fascinating to be able to walk past the front benches and take the same paths out past the counting points into the ‘ayes’ and the ‘nos’ corridors that Members of Parliament use when a debate ends in a division.

All the while the guide gave us delightful anecdotes and historical snippets such as how curtains used to be pulled around the Speaker’s chair so that he could obey the call of Nature without deserting his post, long before women were allowed to become MPs. We left through the gloom of the mediaeval Westminster Hall, one of the few remaining buildings of the original Palace, with its vast hammerbeam roof. It had been a fascinating visit and I would highly recommend it to anyone who is interested in architecture, history or politics, although it has to be said that once inside, we had little opportunity to investigate the building stones. What an interesting day it had been – thank you Eric.

Lynn Everson

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