THE BRITISH GEOLOGICAL SURVEY LEXICON OF NAMED ROCK UNITS

The British Geological Survey’s Lexicon of Named Rock Units at www.bgs.ac.uk/lexicon/home.html provides freely accessible definitions and supplementary information on lithostratigraphical and lithodemic units of Member status, or equivalent, and above used on BGS maps and in BGS publications. It also includes information on some units of lesser rank, notably economically important coal seams and laterally extensive and mappable marine bands, as well as information on names regarded as obsolete or alternative to current names. Currently information is available relating to more than 18 000 unit names, although the level of completeness of entries is variable.

The BGS Lexicon is also used to constrain the rock units that appear on the Survey’s maps, and in reports, geological models and other products and services. A rock unit is not allowable in a BGS product until a definition, at least at an index level, exists within the Lexicon.

The precise nature of a complete Lexicon entry depends upon categorization according to a theme (Bedrock, Superficial, Mass Movement or Artificial) and a detailed class (including Sedimentary Lithostratigraphical, Intrusive Igneous, Lithodemic Metamorphic, and Litho-morph-genetic, among several others). Rank; parent and child units; previous, current and alternative names; age; lithology; environment of deposition / mode of origin; shape; thickness; boundaries; details of type and reference localities and sections; geographical limits of outcrop and subcrop; and associated landforms are all available and searchable information types.

As well as being directly searchable, the BGS Lexicon provides the lithostratigraphical and lithodemic information that backs up other BGS products and services. Notable examples include GeoIndex (www.bgs.ac.uk/GeoIndex/), the DiGMapGB digital geological map suite of products (www.bgs.ac.uk/products/digitalmaps/home.html), and the GeoSure UK geological hazard data sets (www.bgs.ac.uk/products/geosure/home.html). In the near future we intend to enhance the Lexicon’s coverage of the UK continental shelf, so that stratigraphical definitions of on- and offshore units are available to a consistent standard.