An introduction to 1:50 000 Scale Geological Maps
Geological maps show the occurrence, nature, extent, structure and relative (that is, stratigraphic) age of rocks in a district. Maps may be produced in different versions. Beginning in 2003, new maps and new editions of older maps will be described as 'Bedrock' (replacing 'Solid') and 'Superficial Deposits' (replacing 'Drift'), and the combined map as 'Bedrock & Superficial Deposits'. Until this replacement is complete, all the existing maps will be available in their current editions. 'Bedrock' (formerly 'Solid') maps show only the bedrock geology; for example, while 'Bedrock & Superficial Deposits' (formerly 'Solid & Drift' or 'Solid with Drift') show the bedrock geology together with the deposits which may overlie the bedrock. These usually unconsolidated deposits include glacial and postglacial deposits although artificial deposits, such as landscaped, worked and made ground are also shown.
For some areas drift-only maps are produced, notably, for Northern Ireland.
For England and Wales (and Northern Ireland), map sheets normally cover an area 30 km east-west and 20 km north-south; in Scotland the coverage is 20 km east-west and 30 km north-south. The 1:50 000 geological map grids are based on an early Ordnance Survey 1:63 360 (one inch to one mile) scale map grid and are not related to the current Ordnance Survey 1:50 000 map sheets.
'Special' geological sheets are produced for areas of high geological interest which are covered by more than one individual map sheet. They provide a composite map of the district and may be available in different versions.
'Provisional' maps are published for areas where old maps have not yet been fully revised and where resurvey work is unlikely to be completed for several years. They are indicated by 'P' in the lists.
'Facsimilie' maps: during the late 1980s several out-of-print one-inch scale maps were photographically enlarged to 1:50 000 and reprinted as facsimile copies without map revision. These are indicated by the letter 'F' placed after the original publication date of the map (eg 1990F).
Most maps are available in flat or folded format: except for Provisional maps, all folded maps have a card cover.