Bucks Earth Heritage Group

Whitby Formation (Upper Lias)

The muddy limestones of the Upper Lias are the oldest rocks in Bucks - 190 million years old. Exposures are only temporarily available in trenches or road works, or in river banks. The fossils show this was a warm sea close to land - hence the high proportion of clay.

The Upper Lias can occassionally be found in the banks of the River Ouse near Haversham Mills. Although the section is degraded the layers of muds, marls and thin limestone bands can be seen if water levels are low. These are mid- to pale-grey clays and pale-grey limestones. Fossils are present in the form of broken shells (various bivalves as well as some trace fossils including burrows. Ammonites have been found in these rocks in the past). Access to the rocks is not easy, unless water levels are very low. Therefore, it is not recommended that visitors attempt to sample the rock layers due to the potential of falling in the river.