The north western part of Cambridgeshire is where the oldest rocks in the county, from the Jurassic period, are at or near the surface. These rocks are also the most valuable in the county as the source of building material as they include high quality limestone, such as Barnack Rag, Collyweston Slate and Alwalton Marble (all forms of limestone despite their names), and extensive supplies of Oxford Clay, used for brickmaking. The River Nene flows eastward from the ‘uplands’ of Northamptonshire, crosses the Fen Edge at the city of Peterborough, and then crosses Fen Basin before entering the North Sea at the Wash. There are significant gravel deposits along the Nene Valley around Peterborough and Whittlesey and these date from the Pleistocene (Ice Ages).
Peterborough Museum (run by Vivacity) has excellent displays on the Jurassic of Peterborough including large marine reptiles, such as the famous Plesiosaurs and Pliosaurs, as well as the very large fish Leedsichthys. They also have a very good website.
GeoPeterborough is a local partnership promoting geoconservation in the area particularly through the designation and monitoring of Local Geological Sites (RIGS). See the GeoPeterborough website.
Lincolnshire Limestone at Swaddywell Pit Local Geological Site and Nature Reserve, north west of Peterborough
Sands of the Jurassic Grantham Formation under the Lincolnshire Limestone at Swaddywell Pit.