Then deep seas, Gault Clay and the Upper Greensand deposits form the deep soil, more evident where erosion has taken place on steeper hillslopes in the civil parish. The Gault Clay contains phosphate-rich nodules in discrete bands and has a rich marine fauna with abundant ammonites, bivalves and gastropods. The Upper Greensand comprises a variety of sediments with fine silts at the base, giving way upwards into sandstones. Just before the paleogene which included the mass-extinction event of the non-avian dinosaurs, sea levels dropped, exposing Sussex and Kent; marine Upnor Beds were deposited in Surrey. In the paleogene, Southern England slightly rose and the seas retreated and reddish and mottled clays of the Reading Beds were deposited by a large river sand delta system including across much of the Weald (which covers much of Sussex and Kent as well). Later, a rise in sea level around 50 million years ago caused widespread deposition, until 2 million years ago, of the London Clay across the county. The London Clay is a bluish-grey marine clay with isolated pockets of fossils especially where chalkier. The youngest part of the London Clay is known as the Claygate Beds and sand and soft sandstone of the Bagshot Formation, though in many areas such as this generally eroded, followed in most cases by a variable thickness of organic humus.