This layer of the map based index (GeoIndex) shows areas covered by explanatory sheet Memoirs, along with basic information such as memoir title and publication date. The memoirs themselves,compiled by BGS geologists, date from the late 1890s to present day and provide a comprehensive and detailed account of all aspects of the geology of the areas covered by the 1:50,000 (and 1:63,360) map series. Some memoirs may cover more than one geological sheet area and a few cover key geological themes (eg Jurassic rocks) across a large region. Sheet Descriptions are fully colour-illustrated, shortened accounts of the geology that are available for some of the newer published geological sheets.