Geology of the Bath area: Introduction
|This topic provides a summary of the geology of the Bath area – covered by the British Geological Survey
1:50k geological map sheet 265.
Authors: A J M Barron, T H Sheppard, R W Gallois, P R M Hobbs and N J P Smith (BGS).
This topic provides a summary of the geology of the area covered by geological 1:50 000 Series Sheet 265 Bath. The main population centres are the eastern suburbs of Bristol together with Chippenham, Melksham, Corsham and the city of Bath itself, which is England’s only World Heritage City. The majority of the district is however rural, and it lies at the southern end of the Cotswold Hills Area of Outstanding Natural Beauty (AONB). The Cotswold escarpment is the most significant principal geomorphological feature of the district, forming a prominent ridge which runs north from Upton Chew to Old Sodbury. This separates the low-lying undulating ground in the west from the rolling, upland country of the Cotswold Hills, which then fall gently eastwards towards the Avon valley. In the east, the ground rises towards the Chalk downlands of Salisbury Plain.The principal river of the district is the River Avon which enters the north of the district, following a circuitous route through Chippenham, Melksham and Bath to the western edge of the district at Keynsham. The Cam Brook and By Brook are significant tributaries, both entering the river at Bath.
The bedrock of the Bath district includes rocks of Palaeozoic and Mesozoic age, spanning at least 300 million years of Earth history. Strata of latest Silurian age are present at depth. The oldest exposed rocks are of Devonian age, and represent the sedimentary deposits of rivers and coastal plains. These are succeeded by Carboniferous strata formed in tropical seas, brackish-water deltas and freshwater swamps, and much affected by earth movements at the close of the Carboniferous and intermittently thereafter through the Mesozoic. Overlying Triassic rocks were deposited in arid, desert environments, but marine conditions returned in the Jurassic and Cretaceous and these successions were laid down in subtropical seas. All these units are mantled by Quaternary (superficial) deposits on hillslopes and in the major river valleys. Slope failure (mass movement) is a significant feature in the Bath district, and a number of large landslides, also of Quaternary age, are preserved in the area around Bath and along the Cotswold and Corallian escarpments.
The geology of the district has been exploited by man for many centuries. Extensive underground workings and quarries supplied the famous ‘Bath Stone’ for building, whilst the Carboniferous rocks in the west of the district have been mined for coal. Today, the Middle Jurassic succession forms an important aquifer in the district, and the hot springs at — Bath, used for medicinal and recreational purposes since Roman times, draw many visitors to the city.
Summary of the geological succession in the Bath area