The fossils from the lower Eocene rocks indicate a moderately warm climate, the tropical or subtropical flora.

Though sea levels changed during the deposition of the clay, the habitat was generally a lush forest – perhaps like in Indonesia or East Africa today – bordering a warm, shallow ocean.

Once clay is exposed to atmospheric oxygen, framboidal pyrite with a great specific surface is rapidly oxidized.

Pyrite oxidation produces insoluble brown iron oxyhydroxide (FeOOH) and sulfuric acid leading to the formation of relatively soluble gypsum (CaSO4·2H2O, calcium sulfate dihydrate).

This latter is more soluble and mobile than iron oxides and can further recrystallize to form larger crystals sometimes called selenite (coming from the moon, but not related to selenium, although the etymology is the same), or "waterstones".

Large septarian concretions, produced by microbial activity (oxidation of organic matter) in the ancient seafloor during clay early diagenesis, are also common.

[2] It is not frequently exposed as it is to a great extent covered by more recent Neogene sediments and Pleistocene gravel deposits.

Each cycle begins with coarser material (sometimes including rounded flint pebbles), followed by clay which becomes increasingly sandy.

As a result, many insurance companies have now increased the cost of premiums for buildings located in the most susceptible areas where damage occurred, where the clay is close to the surface.

[10] Some 350 named species of plant have been found, making the London Clay flora one of the world's most diverse for fossil seeds and fruits.