Belfry Bulletin Vol. 2 No. 11
BRISTOL EXPLORATION CLUB
May 1948
Editor’s Notes Apologies are due for the long gap between this and the last B.B. I must crave your indulgence as I have been (and still am studying very hard and have little time). However, now the Hon. Sec. is back in circulation I hope the issues will be more regular. The Hon. Sec. has asked me to print the following: I should like to thank everyone for their kind enquiries during my illness. Thanks are also due to Jimmy Weekes who took over my job at a minutes notice and kept the flag flying during my stay in Cornwall. To all those who have been waiting for letters etc., I apologise for the delay and will do my best to work off the arrears of correspondence in a few days. If you do not hear in a reasonable time drop me a reminder, as it is possible that some letters may be mislaid. T.H. Stanbury. Hon. Sec. //-//-//-//-//-//-//-//-//-//-//-//-//-//-// Elementary Geology for Beginners. By another Beginner. R.A. Setterington PreCambrian
METAZOIC
Cambrian Ordovician Silurian
PRIMARY
Devonian & old Red Sandstone Limestone Millstone Grit Coal Measures Permian SECONDARY TERTIARY QUATERNARY
The Earth is roughly 1,000,000,000 to 2,000,000,000 years old. We can obtain an idea of this age from the comparison of putting a postage stamp on a penny on top of Nelson’s Column, then the stamp represents the age of man, the penny the time that animal life has been in existence on the earth, and the height of the column itself the age of the Earth. The rocks which form the surface of the earth are divided into two main types; igneous (plutonic) and sedimentary. The igneous rocks are the rocks which were formed by the original solidification of the earth’s surface, while the sedimentary rocks are those formed by erosion and subsequent deposition under the sea or other body of water. These two main divisions are further separated as shown in the attached table. The secondary and tertiary rocks are further subdivided into 18 different types of rock, three of which are not represented in Great Britain, but since this division only confuses the investigator it is not made here. The sedimentary rocks were laid down, in strata, on top of the igneous rocks in order, (from top to bottom in the diagram) so that we might expect that if we dug down into the earth’s surface we would pass through each layer in turn, the nearest first. However, owing to distortion, faulting and erosion of the earth’s surface this does not happen. If we look at a geological map of Great Britain we find that in the extreme west the rock have been eroded that only the igneous rocks and early sedimentary rocks remain while in the east very little erosion has taken place. Roughly speaking the older rocks occur, in Scotland, north of the line Greenock – Dundee; in Wales, all except the north-east corner and a larger area in the south and in Devon and Cornwall in England. The newer rocks occur in England south and east of a line from Stockton south to Nottingham and south west to the Severn, leaving out two small areas in central and southeast Devon and the Mendips. Thus we see that is useless to expect to find limestone caves in other areas than: -
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Central and South east Devon The Mendips South and North-east Wales Derbyshire Lancashire West Yorkshire, and an area north to the Cheviot Hills An area around Edinburgh and Glasgow
However limestone is not the only thing necessary for the formation of caves; water is also needed to dissolve it away and leave cavities. The water which form caves comes, originally from rain and rain is heaviest in hilly or mountainous districts. The caves in Yorkshire and Derbyshire differ from those in the Mendips in configuration, due to the differences of the angle in the strata. In Yorkshire the strata is horizontal or nearly so, this causes the caves to occur as long vertical pitches and nearly horizontal passages. In Mendip the strata dips towards the edges of the hills, this is because the Mendips are an uplifted ridge of strata. The Mendips were originally a lot higher than they are now, but they have been eroded so much on top that the tops of the higher parts (like Blackdown and Ninebarrows) are old red sandstone. Now sandstone is permeable to water but is not dissolved by it, the shales (which lie over it in geological time, around it in physical position) are impermeable, so rain falls on the sandstone it passes through it and drains out through springs (like Ladywell) passes over the shales and into limestone. From this we can see that the best place to look for swallet caves is at the junction of the shales and the limestone. This conclusion is amply born out if we consider the row of caves: - Cuckoo Cleeves, Plantation Swallet, Eastwater, Swildons and Hollowfield. The water, having passed through limestone, must come out somewhere and this is does at caves of influx, like Wookey Hole and Cheddar, and springs, like Rickford and Rodney Stoke. The Geology of Wookey Hole is worth a special mention. Wookey was a very old cave when the Mendips were relatively young, then the hills sank down into the sea and the gorge which the river had formed was filled up with a mass of conglomerate. The hills then rose out of the sea again and the river had to form a new cave and gorge, this is why Wookey Hole is in conglomerate. &&&&&&&&&&&&&&&&&& Note: - Dolomitic Conglomerate is composed of debris of denudation, a mixture in the case of Wookey, of limestone and sandstone fragments some large some small, all bound together into a solid mass. A very good analogy being a mass of concrete viewed through a magnifying glass. (Ed.). ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The Annual general Meeting of the CAVE RESEARCH GROUP will be held at Sheffield on June 10th. 1948 at 6.p.m. Will anyone wishing to attend please let the Hon. Sec. have his name as soon as possible, so that necessary arrangements can be made. %%%%%%%%%%%%%%%%
Report on exploration and survey of a Chalk Mine near Springfield, Rickmansworth, Herts by G.W. Ridyard. I decided that, whilst I was at home this Easter, I would have a look at a chalk mine which is in our neighbourhood. This mine consists of a vertical shaft which was once some 50ft. deep, but which is now shortened to approx. 40ft. in depth by a large accumulation of muck and rubble at its foot. Branching out from the bottom shaft are a series of interesting chambers hewn out of the chalk strata. The farmer who rents the land told me that the pit together with several others nearby, which are now filled in, were dug within the last 100 years to provide chalk for spreading on sour ground. This sound quite feasible and put an end to my hopes of an ancient flint mine, which in West Hertfordshire would have been quite a find. However, I thought it was still worth having a look at so on Good Friday afternoon my friend, Douglas Geoff, and I lugged two sections of rope ladder and a tether to the hilltop where the shaft is situated.
BB11. 3 The top of the shaft is surrounded by trees so we had no difficulty tethering the ladder quite securely. The ladder was just long enough and, because of the slight overhang at the top of the shaft, was clear of the wall most of the way down. At the foot of the ladder one could see that the shaft is circular in section and it gave one the impression of being at the bottom of a well. The pile of debris is quite large and extends for some feet into the chambers on either side of the shaft. As might be expected there were numerous animal bones, old cans, tyres and ‘what have you’ mixed up with the dirt in the pile. The chambers average 6-8ft. in width and are between 15-20ft. in height. The cross-section of the chambers is more or less Gothic-vertical sides with two arcs at the top to form the roof - and this coupled with complete silence makes you feel you are in a deserted church. The floor is very even in most places and the whole system is surprisingly dry. I had taken some collecting bottles with me in case there might have been some ‘bugs’ for E.A. Glennie, but place seemed much too dry to attract cave fauna. I saw no signs of bats anywhere in the system. After spending a couple of hours on the survey of the place with pocket compass and knotted cord, we decided we had found out just about all there was to know about the place and we beat a retreat. Both Geoff and I enjoyed exploring this place and although I had hoped it might have more possibilities I shall not be nagged by the thought that I might be missing something worth-while as I might have been had I not have gone down. %%%%%%%%%%%%%%%%%%%% Geoff has sent me a very fine plan of the above Chalk Mine. Space will not allow the printing of it but it will be in the next issue. ********************************* List of Members No.2 L. Peters, 21. Melbury Road, Knowle, Bristol. 4. J.C. Weeks, 376. Wells Road, Knowle, Bristol. 4. R.A. Crocker, 5. Bury Lane, Horfield, Bristol. 7. R. Woodbridge, 384. Wells Road, Knowle, Bristol. 4. D.A. Bessell, 5, Albert Place, Redfield, Bristol. 4. A.E. Baxter, 92. Redcatch Road, Knowle, Bristol. 4. E. Knight, 48. Grafton Street, St. Philips Marsh, Bristol. R. Brain, 10. Western Ave. Cossham Road, St. George, Bristol. 5. Mrs I.M. Stanbury, (Life Member) 74. Redcatch Road, Bristol. 4. A. Atkinson, 32. Salisbury Road, Redland, Bristol. ********************************** The Belfry, through the generosity of Sett and Postle (to the uninitiated R. A. Setterington and T.M. Thompsett) has had a radio presented to it. Thanks also to Dick Bellamy who also offered one. A copy of British Regional Geology, Bristol and Gloucester District has been presented to the library by Pongo (R.M. Wallis). ********************************** Back numbers of this Bulletin can be obtained, when in print, from the Hon. Sec. at 3d. per copy, 4d. post free. Also in stock are: - Carbide Lamp, Spare jets, rubber gaskets and prickers. Caving Hats and Caps together with all caving and camping gear can be obtained through the Hon. Sec., who also has Y.H.A. & Camping Club Application Forms.
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