The Pocket Park lies over limestone rocks dating from the Jurassic period 135 to 190 million years ago, the same geology that forms the belt that stretches almost continuously from Lyme Regis in Dorset to the Cleveland Hills in Yorkshire. Within the past two million years Britain was covered by thick ice sheets. There were four glacial advances in Britain, the most recent one, called the Devensian dates from 26,000 -10,000 years ago, but it didn’t reach Northamptonshire. Our area then lay in a zone of permafrost to the south of the maximum extent of the ice sheets.
Earlier and more extensive glacial advances brought enormous quantities of rock material scoured from distant sources including the Jurassic rocks of Yorkshire, the Chalklands of Lincolnshire, the Carboniferous rocks and the Triassic sandstones and igneous rocks of Leicestershire as well as a wide variety of clays and ironstones from the locality. This material is our grey subsoil known as boulder clay containing rounded pebbles of these rock types which can be seen clearly in the soils over all the area around Yelvertoft.