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| Keywords: The Quarterly journal of the Geological Society of London (12711373265).jpg PRESTWICH SAND- AND GRAVEL-PIPES <br> 71 <br> line m n is perfectly straight This section also corroborates the <br> inference drawn from fis- 1 <br> Fig 2 Section of the upper part of a Sand-pipe in the Chalk <br> at Grays <br> Drawn on the same scale as Fig 1 <br> n Thanet Sands <br> b Seam of clay and sand with green-coated flints <br> c Gravel d Chalk <br> The general arrangement is the same in the gravel-pipes only it is <br> rougher and less apparent ; for as the gravel is usually spread over <br> the chalk in a large unstratified sheet of one rough homogeneous <br> structure throughout it necessarily follows that however slow its <br> subsidence at any point into a pipe penetrating the chalk may have <br> been the absence of straight lines of bedding would prevent the <br> clear exhibition of any lines of flexure in the gravel of the pipes <br> and would cause it to retain the same apparent want of structure <br> which characterises the mass of the gravel itself But it sometimes <br> happens that the gravel is roughly stratified or rather spread out in <br> layers of variable texture ; or at times a bed of sandy gravel full of <br> Tertiary flint-pebbles overlies another bed containing almost solely <br> subangular and unrolled flints In cases where pipes have been <br> formed under such gravels the curved or inverted conical ar- <br> rangement of the mass and the descent of the central core from <br> the higher beds generally become apparent as in the sand-pipes <br> Some good examples of these pipes are common on the Chalk downs <br> especially in some pits above Westerham and Wrotham The sides <br> of most of these pipes are there formed of an extension of the layer <br> of perfectly angular flint-rubble 1 to 4 feet wide occurring at the <br> base of the drift whilst the core consists of worn gravel or often of <br> round flint-pebbles and sand derived from the Tertiary beds which <br> formerly overspread that area <br> The size of the sand- and gravel-pipes is very variable some being <br> only a few feet deep and others reaching to a depth even of 100 feet <br> or more with a diameter'of 20 to 40 feet They are very common all <br> over the Kent and Surrey Chalk district ; also in Berkshire Wilts <br> There are some very good instances of gravel-pipes in the Chalk-pits at Green- <br> hithe The neighbourhood of Watford Henley and the Downs a few miles N E of <br> Maidstone also offer convenient localities for studying this phenomenon ; there <br> are in fact few places in the Chalk district where it may not be observed to a <br> greater or lesser extent 35614637 110213 51125 Page 71 Text v 11 http //www biodiversitylibrary org/page/35614637 1855 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 11 1855 Geology Periodicals Smithsonian Libraries bhl page 35614637 dc identifier http //biodiversitylibrary org/page/35614637 smithsonian libraries Information field Flickr posted date ISOdate 2014-02-23 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12711373265 2015-08-26 20 58 27 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1855 Photos uploaded from Flickr by FĂŚ using a script | ||||
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