The Eocene Succession in the Eastern Part of the Enborne Valley, on the Borders of Berkshire and Hampshire

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Abstract
Summary: Records obtained from trial borings with a combined penetration of over 8000 feet of strata are analysed, and an account is given of the Eocene succession revealed. This ranges from the Lutetian to the Sparnacian, comprising the Bracklesham, Bagshot, London and Reading formations. Their maximum proved thickness is 436 feet. The Chalk next beneath the Eocene is that of the Marsupites Zone except in the most northerly boring, where the Uintacrinus Zone was proved. Evidence is adduced suggesting that local variations in the thickness of the Reading Beds may be due to original irregularities on the surface of the Chalk. The Reading Beds, averaging 69 feet thick, have a marine “bottom bed” which varies in thickness from 6 to 25 feet; in one case this facies seems to persist to within 10 feet of the top of the series, foraminiferal glauconitic sand there replacing the mottled clay of nearby borings. Several seams of lignite were found, one of them resting on a seat-earth full of pyritized rootlets. The lithology of the rest of the succession resembles Wat of the Hampshire Basin rather than that of the London Basin of which it forms a tectonic part. Alternations of marine and estuarine episodes recur throughout; banks of shingle are common and beach-deposits occur; lignite, scattered or in actual seams, pervades the whole. The London Clay rests on a plane of erosion at the top of the Reading Beds; it falls into three main sections, the Lower Silts, Stiff Clays and Upper Silts.