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    This low-resolution image has been produced from BGS land and marine gravity data. The colour was generated using the BGS COLMAP software package. Colour levels are defined by histogram equalisation. Combining this image with the grey shaded relief image produces a similar image to the colour shaded relief image. The measured gravity values have been corrected in order to show the anomalies attributable to variations in crustal density. In broad terms the blues are attributable to large volumes of low density rocks, the reds to high density rocks. Significant lows occur, for instance, over areas of thick, low density sedimentary rocks(e.g. Cheshire Basin, Wessex Basin), or large granites (eg Cornwall). For marine data, free-air anomalies have been calculated from observed gravity values along marine survey lines. Line intersection errors between crossing lines and overlapping surveys have been used using network adjustment techniques. Free air anomalies have been calculated for sea-bottom stations. For land data, bouguer anomalies have been calculated from gravity observations at points of known height. In order to minimise the effect of topography, Bouguer corrections for the British Mainland have been applied using a density estimated for each station. Elsewhere a correction density of 2.67 Mg/m3 has been used. Corrections for the gravitational effect of terrain have been made where significant, and in a general extent to a radius of 48.6km. The data have been interpolated onto a 1km x 1km grid using a variable tension technique, and smoothed.

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    This layer of the map based index (GeoIndex) providex an index to 17,500 borehole rock samples (drillcore) from the Mineral Reconnaissance Programme (MRP) and related studies. The UK Government's Department of Trade and Industry (DTI) funded BGS to provide baseline information on areas prospective for the occurrence of metallic minerals in Great Britain. This programme, known as the MRP, ran continuously from 1973 to 1997 and covered particular locations across Great Britain. It was designed to stimulate private sector exploration and to encourage the development of Britain's indigenous mineral resources. Under the programme a number of boreholes were drilled to gather information.

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    This layer of the map based index (GeoIndex) shows the location of earthquakes within the UK. The historical catalogue has been compiled, in general, from macroseismic observations (ie felt effects). Before 1700, only earthquakes with magnitudes of 4.0 ML or greater are included. After 1700, all known events with magnitudes of 3.0 ML or greater are included together with some other, smaller ones. Accuracies of magnitude, location, and origin time vary with the quality of information available for this period as they do for instrumental measurements in the post 1970 period. In that case, variations are largely a function of the seismograph station coverage, which has been improving up to the present day.

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    This layer of the GeoIndex shows the localities for which details of identified fossil specimens in the BGS Biostratigraphy Museum are databased. Only Ordovician and Silurian specimens listed currently. Samples and taxonomic identifications will be listed and will in future be able to be queried using the query-by-attribute tool to the right of the map. See also Fossil Localities. Material is available for inspection on application by e-mail; it is free for academic research but is charged for commercial work. Specimens are sometimes available for loan to bona fide academics.

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    This layer of the map based index (GeoIndex) shows sites where regularly monitored rest water level data are available, usually covering a long time period. The data shows seasonal fluctuations in the water table and responses to periods of high or low rainfall.

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    The map based index includes outlines for some 8,000 opencast coal prospecting sites dating from the 1940s until the mid 1990s. The index leads to information on the records of some 1 million boreholes (additional to those shown in the Borehole Records layer) drilled during site exploration and also the accompanying plans and other data, all filed in 3,618 boxes. The sites include those that have been drilled and not worked and also those that have been exploited. The original data, hardcopy maps, were received from the Coal Authority in 2001.

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    This layer of the Map based index (GeoIndex) shows the location of available UTM (Universal Transverse Mercator) series 1:250000 geological maps. These maps display Bedrock, Quaternary (Superficial deposits) geology of the offshore areas and Seabed Sediments of the UK landmass and offshore regions. The different versions are normally published as separate maps for land areas, but these may be combined on a single map for offshore areas. Maps are normally available in flat and folded format. The UTM Series (Universal Transverse Mercator projection) maps cover an area of 1deg. latitude by 2deg. longitude.

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    This layer of the map based index (GeoIndex) shows the location, with basic metadata, of selected DECC (Department of Energy & Climate Change) offshore hydrocarbon wells. The source data for this layer was downloaded from the DECC website at www.og.decc.gov.uk/information/maps_offshore.htm. These are DECC owned data and information and supply of the actual data is through the DECC release agents.

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    This layer of the Map based index (GeoIndex) shows the location of registered samples of drillcore and washed cuttings from onshore boreholes drilled in UK by BGS, commercial and public bodies, representing almost 10,000 boreholes. There is also a drillcore collection taken from onshore boreholes drilled in England and Wales by the BGS and commercial and public bodies.

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    This layer of the map based index (GeoIndex) shows the location of onshore UK boreholes known to BGS that have digital or paper geophysical borehole logs. The details given for each borehole are, the name of the borehole, the grid reference and the format, ie. paper or digital. Scattered distribution of boreholes, locally dense coverage, few logs from Scotland. The GeoIndex is updated at regular intervals but more information may be available than is shown at any one time.