 Commercially useful deposits of about 2m to 4m thick are present in Kent, Hertfordshire and Hampshire, overlying chalk, Thanet Beds or London Clay.The original deposition of the sediments occurred under cold climates where fluvial out-wash sediments from glaciers were subject to windy dry periods.The exposed finer-grained sediments were picked up and transported by the wind and were deposited wherever the wind strength decreased.