Greensand is an olive-green coloured
sandstonerock which is commonly found in narrow bands, particularly associated with bands of chalkand clayworldwide; it has been deposited in marine environments at various times during Earthhistory, such as during the Jurassicand Cretaceousperiods.
Formation and locations
Greensand forms in anoxic marine environments that are rich in organic detritus and low in sedimentary input. Greensands are occasionally fossil-rich, such as in the late Cretaceous deposits of
New Jersey. [Dale A. Russell, "An Odyssey in Time" (Toronto: University of Toronto Press, 1989), pp. 137-9.] Important exposures are known from both northern and western Europeand North America.
Great Britain, Greensand usually refers to a specific geologic formation of Lower Cretaceousage. A distinction is made between Upper Greensand and Lower Greensand; the term Greensand was originally applied by William Smith to glauconitic sandstones in the west of England and subsequently used for the similar deposits of the Weald, before it was appreciated that the latter are actually two distinct formations separated by the Gault Clay. [Gallois R.W. & Edmunds M.A. (4th Ed 1965), "The Wealden District", British Regional Geology series, British Geological Survey, ISBN 011884078-9]
Both Upper and Lower Greensand outcrops appear in the scarp slopes surrounding the
London Basinand the Weald.Prominent seams are to be found in the Vale of White Horse, in Bedfordshire, in Kent, Surrey, the South Downs National Park[ [http://www.southdowns.gov.uk/content/page/1249/LCA_N.pdf South Downs Integrated Landscape Character Assessment ] ] and Hampshireand the Jurassic Coastin Dorset.
The soil of the greensand is quite varied, ranging from fertile to fairly sterile. On the fertile soils
chestnutand stands of hazeland oakare common, while Scots Pineand Birchcolonise the poorer soils.Greensand Way in Kent, 1992, Kent Count Council, ISBN 1-873010-23-0] These Greensand Ridges are popular long distance walking routes, for instance the Greensand Wayin Kent.
The Lower Greensand (known as the Woburn Sand north of the
London Basin) is of Aptianage. In the Weald the Lower Greensand consists of four deposits which are partly diachronous: the Atherfield Clay15-50 ft thick, the Folkestone Beds60-250 ft thick; the Hythe beds60-350 ft thick and the Sandgate Beds5-120 ft thick. Britain's Structure and Scenery, L.Dudley Stamp, Pub Sept 1946, Collins New NaturalistSeries. ] Although it appears both north and south of the London Basin it is not present everywhere beneath the chalk which underlies the basin; the Gault lies directly on eroded Jurassicor Devonianrocks under much of the area.
The Upper Greensand is of
Albianage. It is classed as part of the Gault Formation, representing a sandy faciesdeposited in areas of stronger currents than the Gault Clay. Like the Lower Greensand it is not present beneath the whole of the London Basin, apparently passing laterally into Gault clay east of a line between Dunstableand Tatsfieldand of uncertain extent to the east of London. [Sumbler M.G. (1996), "London and the Thames Valley", British Regional Geology series, British Geological Survey, ISBN 0-11-884522-5] [Ellison R.A. et al 2004, "Geology of London: Special Memoir for 1:50,000 Geological sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)", British Geological Survey, Keyworth, ISBN 0-85272478-0]
Outcrops of the Upper Greensand occur in the south-west of England including the
Blackdown Hillsand East Devon Plateau and the Haldon Hills, remnants of a once much wider extent. [Edmonds E.A.,McKeown M.C. & Williams M. (1975), "South-West England", British Regional Geology series, British Geological Survey, ISBN 0-11-880713-7]
Properties and uses
The green colour of greensand is due to variable amounts of the
mineral glauconite, an iron potassium silicatewith very low weatheringresistance; as a result, greensand tends to be weak and friable. It is a common ingredient in garden fertilisers, such as in organic gardeningand organic farming. Due to its chemical exchange properties, the glauconite of greensand is used as a water softener. Greensand coated with manganese oxide, known as manganese greensand, is used in well water treatment systems to remove insoluble ferric (oxidized) iron and manganese. It is also used as a type of rock for stone walls in areas where greensand is common.
In Roman times coarse grits derived from the lower greensand were used to line the inner surface of mortaria (grinding bowls) produced in the Oxfordshire pottery kilns. [Henig M. & Booth P. (2000), Roman Oxfordshire, pg.166]
* [http://www.state.ar.us/agc/greensan1.htm Arkansas Geological Commission, "Greensand".]
* [http://www.1911encyclopedia.org/Greensand Encyclopaedia Britannica/Greensand]
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Look at other dictionaries:
Greensand — Green sand ( s[a^]nd ), n. (Geol.) A variety of sandstone, usually imperfectly consolidated, consisting largely of glauconite, a silicate of iron and potash of a green color, mixed with sand and a trace of phosphate of lime. [1913 Webster] Note:… … The Collaborative International Dictionary of English
Greensand — (Geogn.), so v.w. Grünsand … Pierer's Universal-Lexikon
Greensand — (spr. grīn ßänd), soviel wie Grünsand, s. Grünerde und Kreideformation … Meyers Großes Konversations-Lexikon
Greensand — Greensand, s. Grünsand … Lexikon der gesamten Technik
greensand — [grēn′sand΄] n. a green, sandy deposit containing much glauconite … English World dictionary
greensand — /ˈgrinsænd/ (say greensand) noun 1. a sandstone containing much glauconite, which gives it a greenish hue. 2. moulding sand, rich in organic matter, as used in a foundry … Australian English dictionary
greensand — noun Date: 1699 a sedimentary deposit that consists largely of dark greenish grains of glauconite often mingled with clay or sand … New Collegiate Dictionary
greensand — /green sand /, n. a sandstone containing much glauconite, which gives it a greenish hue. [1790 1800; GREEN + SAND] * * * … Universalium
greensand — noun A greenish sandstone containing glauconite … Wiktionary
greensand — noun Geology a greenish kind of sandstone, often loosely consolidated … English new terms dictionary