There are many rocks from the tertiary period in London, the most famous being London clay, which is a marine geological formation and is rich in fossils. This rock is very important, because, due to the fact that it can be up to 150 metres thick, it supports most of the tunnels that exist through London most famously the London underground. It is thick and blue for the most part, and is unique to London and some of the areas around it. The rock was originally deposited by the sea, and through many cycles of deposition, ended up in London. Other rocks from the Tertiary period in London include sand, and a different typed of clay which belongs to a group called the Lambeth Group. These were from a tropical sea environment, shown by fossil evidence. Some of the fossils they have found there include freshwater animals. There is also the Bagshot Beds (now called the Wittering Formation) which are cross-bedded sands with thin clay 'bands'. There is little evidence which tells us where they are from, but geologists guess that they were deposited by an inshore sea, and finally there is the The Bracklesham Beds (now called the Marsh Farm Formation), which comprise of clays and sands from the sea . They can be up to 60 metres thick.
To find these rocks you can be almost anywhere in London.