English: Sequence of Paleogene strata exposed at the edge of Gilbert's Pit SSSI in Maryon Park, Greenwich, London The grey sand making up the lower two-thirds of the old quarry face is the Thanet Formation , This is overlain by the yellow-brown weathering sands of the Upnor Formation (the lower part of the Lambeth Group ). The overlying Woolwich Formation consists of the distinctive light grey shell bed, followed by dark grey clays. The top of the slope has the distinctive black flint pebbles of the Harwich Formation (better known locally as the Blackheath Beds)