Geology Site Account

Ingatestone borehole (site of)

This borehole was sunk in 1902 at the new Ingatestone Waterworks to provide a water supply for the town. The borehole was 260 metres (800 feet) deep and recorded an exceptional thickness of London Clay (approx 150 metres or 500 feet). It is impossible to explain this anomaly other than by the presence of a fault. A fault is a fracture along which the rocks have moved relative to one another and in this case the borehole must have intercepted an inclined fault plane, thus encountering a repetition of a section of London Clay strata. Movement of rocks along faults usually cause earthquakes and this fault may have been responsible for a local earthquake in the distant past.

The site of the borehole was visited by the Geologists Association in 1906 which was attended by William Whitaker, a geologist from the Geological Survey who made a special study of boreholes and wells. The engineer of the Waterworks exhibited samples of the strata from various depths and members were able to examine sections of the bore that had been laid out in the adjoining field. The borehole passed through London Clay, Reading Beds and Thanet Sands into the Chalk, which it penetrated for 50 metres (150 feet) before encountering an adequate supply of water.