Tedbury Camp is located at the eastern end of the Mendip Hills, on the northern limb of the Beacon Hill pericline. The core of the pericline comprises Silurian volcanics and Devonian clastics that are poorly exposed apart from occasional quarries. The overlying Lower Carboniferous succession is dominated by limestones which have been extensively quarried and are therefore well exposed, although access to the largest ‘super-quarries’ is restricted by operations. The undulating ground to the north of the Mells Valley is occupied by Upper Carboniferous Coal Measures, but outcrops are very infrequent and information is gained primarily from old coal mining records. The Palaeozoic succession in this area dips steeply to the north and is locally overturned and thrusted in response to Variscan deformation. Isolated patches of terrestrial Triassic red beds and marine Jurassic sediments occur in the area between Mells and Frome, but a more extensive cover of Jurassic and Cretaceous is preserved to the east of Frome (Figure 4). The unconformity between the steeply dipping, deeply eroded Carboniferous limestones and the sub-horizontal Mesozoic rocks is a conspicuous feature in many quarries and natural exposures in the area. More detailed accounts of the regional geology are provided by Green (1992), Hardy (1999) and Farrant (2008).

The overstep of the Mesozoic rocks onto the eastward plunging nose of the Beacon Hill pericline is evident. At Tedbury Camp (arrowed) the Holkerian (Lower Carboniferous) Clifton Down Limestone (CDL) is overlain unconformably by Bajocian (Middle Jurassic) Inferior Oolite (InO). Reproduced from the Frome Sheet 281 (2000) with the permission of the British Geological Survey © NERC. All rights reserved.