It is at Seaton Hole at the western end of Seaton Bay that the geology changes dramatically with the white chalk and Upper Greensand to the west and the lower red Mercia Mud stone cliffs to the east.

The Mercia Mud stones cliffs are 225 million years old and were formed by mud being deposited on the beds of shallow lakes in the Triassic period. This mud has been hardened into the ‘mudstone’ we see today.

The Cretaceous sea flooded over the area 100 million years ago, firstly depositing sand which hardened into the 'Upper Greensand' followed by lime mud's which became the strata of Beer Limestone and then over millions of years the algal coccoliths that formed the pure white chalk.

Both of these types of rock strata can be seen at the Seaton Hole ‘fault’ where the continuity of the rock layers have been ‘broken’ with the younger white Cretaceous rocks dropping down 60 metres to the level of the much older red Mercia mudstone rocks of the Triassic period.

Eastwards from Seaton Hole the red Mercia Mud stone cliffs disappear beneath the flood plain of the River Axe emerging once more in the lower layers of Haven Cliffs on the east bank of the estuary.

Here the older Mercia Mud stone of the Triassic period is capped with younger layers of Fox mould or Gault, Upper Greensand and chalk from the Cretaceous period.