BGS Geology - 625k (DiGMapGB-625) 2008

Data identifying landscape areas (shown as polygons) attributed with geological names. The scale of the data is 1:625 000 providing a simplified interpretation of the geology and may be used as a guide at a regional or national level, but should not be relied on for local geology. Onshore coverage is provided for all of England, Wales, Scotland, the Isle of Man and Northern Ireland. Data are supplied as four themes: bedrock, superficial deposits, dykes and linear features (faults). Bedrock geology describes the main mass of solid rocks forming the earth's crust. Bedrock is present everywhere, whether exposed at surface in outcrops or concealed beneath superficial deposits or water bodies. Geological names are based on the lithostratigraphic or lithodemic hierarchy of the rocks. The lithostratigraphic scheme arranges rock bodies into units based on rock-type and geological time of formation. Where rock-types do not fit into the lithostratigraphic scheme, for example intrusive, deformed rocks subjected to heat and pressure resulting in new or changed rock types; then their classification is based on their rock-type or lithological composition. This assesses visible features such as texture, structure, mineralogy. Superficial deposits are younger geological deposits formed during the most recent geological time; the Quaternary. These deposits rest on older rocks or deposits referred to as bedrock. The superficial deposits theme defines landscape areas (shown as polygons) attributed with a geological name and their deposit-type or lithological composition. The dykes theme defines small, narrow areas (shown as polygons) of a specific type of bedrock geology; that is igneous rocks which have been intruded into the landscape at a later date than the surrounding bedrock. They are presented as an optional, separate theme in order to provide additional clarity of the bedrock theme. The bedrock and dykes themes are designed to be used together. Linear features data (shown as polylines) represents geological faults at the ground or bedrock surface (beneath superficial deposits). Geological faults occur where a body of bedrock has been fractured and displaced by large scale processes affecting the earth's crust (tectonic forces). The faults theme defines geological faults (shown as polylines) at the ground or bedrock surface (beneath superficial deposits). All four data themes are available in vector format (containing the geometry of each feature linked to a database record describing their attributes) as ESRI shapefiles and are delivered free of charge under the terms of the Open Government Licence.