There are many rocks from before the Tertiary Period, such as old and hard rocks from the Palaeozioc period, found to have existed through Boreholes. These consist of Silurian mudstones and sandstones, generally overlain by Devonian strata which are largely of Old Red Sandstone. Most of these are from the Silurian period, such as mudstones and sandstones, and above them are those from the Devonian period, which consists of red sandstone. These Devonian rocks can only be found in the south of London. The Palaeozoic rocks stretch to the south of England and can be found up to 1000 metres below the English channel. Above all these rocks are Gault clays, which are impermeable. These are from the Cretaceous period. They are about 60 metres thick.
Travelling further up, on top of the Gault clay is a layer of white chalk, which is about 200 metres thick. It is rich in fossils, and includes animals such as clams. There is also an abundant amount of flint at the top of this clay. This clay is the basis of the London Basin.
Travelling further up, on top of the Gault clay is a layer of white chalk, which is about 200 metres thick. It is rich in fossils, and includes animals such as clams. There is also an abundant amount of flint at the top of this clay. This clay is the basis of the London Basin.
To find these rocks, you might want to visit Chiltern Hills in High Wycombe.