Archaeomagnetism: An Error Assessment of Fired Material Observations in the British Directional Database.

The direction of the geomagnetic field in Britain is now moderately well established for the last 2,000 year based on analyses of the directions of magnetic remanence isolated at some 466 archaeological sites in Britain and parts of N.E. France. The vast majority of these observations are of fired, in situ archaeological materials, with only 21 site observations being based on sediments. Most of these findings are only available in virtually inaccessible field reports and theses, or similar such publications, so the summary mean site British values have been placed into a database; this has then been extended to include may directional observations on a global basis. These data are now available as Dbase and Access databases, as well as in ASCII form. It is hoped that such data will enable more detailed secular variation studies to be undertaken and encourage other workers to add their observations to this database, particularly those that may otherwise be observed scatter with that expected from archaeomagnetic, geomagnetic and archaeological site sources suggest that the precision of the mean direction is only a partial estimate of the total error, evaluated as being of the order of +5 for any given site that may have taken place after the last heating. There is also clear evidence for invalid age assignments in some of the published data but increasing archaeomagnetic data are now enabling such errors to be re-evaluated and the technique is thus improving as more data accumulate.