The detail level in each is broadly comparable, but the informal label is applied if definitions do not yet meet all the criteria of modern stratigraphical procedures. Informal definitions may be formalised as mapping progresses and knowledge of the rocks improves. Older full definitions were flagged simply as formal or informal, but it is now recognised that some definitions may be valid only locally, whilst others are of national, or even international, applicability. In the future these distinctions will be recorded. Meanwhile, the full formal and informal definitions can be considered applicable in the areas of the stratotypes described, and potentially across wider geographical extents.
All entries carry a code describing the level of information held.
The database is dynamic, as new entries are added and existing entries are revised, upgraded and reclassified. The Lexicon information is a current BGS interpretation. For information regarding the copyright of BGS material please refer to our copyright page .