THE chalk forming the base of the escarpment between Woolwich and the entrance to the valley of the Ravensbourne, dips at a low angle to the south-south-east under Greenwich Park and Blackheath, where it is overlaid by the Thanet Sands, estimated by Mr. Whitaker of the Geological Survey at 40 to 50 feet, the Reading and Woolwich Beds, consisting of shelly clays, sometimes 40 feet thick, associated near Lewisham with fine laminated sands. These beds are overlain by the Oldhaven or Blackheath gravels, reaching a thickness of about 50 feet, which have been largely dug for gravel in various parts of the district.
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Induced subsurface movements associated with the presence of natural and artificial underground openings in areas underlain by Cretaceous Chalk
Geological Society, London, Engineering Geology Special Publications (1988)