Beneath our feet
Under Peterborough, the land has three main rock types..
Lime-rich mud covered the bottom of Peterborough’s shallow sea, 165 million years ago. Today, the mud has been compressed into limestone.
The limestone is made of tiny balls called ooliths. They formed as the sea gently rolled sandgrains around, gradually coating them in the lime-rich mud.
Bits of broken seashells and corals in the stone show that the sea was shallow and stormy, churning up the mud and the bodies of sea creatures.
Limestone has been a favoured building material since medieval times. Peterborough Cathedral and the museum building show how stonemasons could cut and carve the hardwearing limestone.
A thick layer of clay formed at the bottom of the deep sea that covered Peterborough in the Late Jurassic, 155 million years ago.
When animals died and sank to the soft clay sea floor, they were gradually covered by sediment and preserved as fossils. Now, the clay gives us a record of the sheer variety of life, from spiral-shelled ammonites to the remains of huge marine reptiles.
Today, the dark grey clay is still quarried for use in brick-making. This was a major industry in Peterborough, and many of its houses are made out of Oxford Clay bricks.
Gravel, sand and peat came much later to Peterborough, during the Ice Age 40,000 years ago.
Gravel, sand and peat came much later to Peterborough, during the Ice Age. By this time the land had moved north and risen out of the ancient sea.
The gravel today is extracted and used widely for construction and on driveways.