BAGSHOT BEDS  , in

geology, a series of sands and clays of shallow-water origin, some being fresh-water, some marine . They belong to the upper Eocene formation of the London and Hampshire basins (England), and derive their name from Bagshot Heath in Surrey; but they are also well developed in Hampshire and the Isle of Wight . The following divisions are generally accepted : Upper Bagshot Beds Barton sand, and Barton clay . Middle „ Bracklesham beds . Lower Bournemouth beds, Alum Bay beds, and Bovey Tracey beds (?) . The lower division consists of pale-yellow, current-bedded sand and loam, with layers of pipeclay and occasional beds of flint pebbles . In the London basin, wherever the junction of the Bagshot beds with the London clay is exposed, it is dear that no sharp line can be drawn between these formations . The Lower Bagshot beds may be observed at Brentwood, Billericay and Highbeech in Essex; outliers, capping hills of London clay, occur at Hampstead, Highgate and Harrow . In Surrey consider-able tracts of London clay are covered by heath-bearing Lower Bagshot beds, as at Weybridge, Aldershot, Woking, &c . The " Ramsdell clay,” N.W. of Basingstoke, belongs to this formation . In the Isle of Wight the lower division is well exposed at Alum Bay (66o ft.) and White Cliff Bay (140 ft.); here it consists of unfossiliferous sands (white, yellow, brown, crimson and every intermediate shade), and clays with layers of lignite and ferruginous sandstone . Similar beds are visible at Bournemouth, and in the neighbourhood of Poole, Wareham, Corfe and Studland .

The

leaf-bearing clays of Alum Bay and Bournemouth are well known, and have yielded a large and interesting series of plant remains, including Eucalyptus, Caesalpinia, Populus, Platanus, Sequoia, Aralia, Poly podium, Osmunda, Nipadites and many others . The sands and clays of Bovey Tracey (see BovEY BEns) are probably of the same age . The clays of this formation are of great value for pottery manufacture; they are extensively mined in the vicinity of Wareham and Corfe, whence they are shipped from Poole and are consequently known as "Poole clays "; similarly, " Teignmouth clay" is obtained from the Bovey beds . Alum was formerly obtained from the clays of Alum Bay; and the lignites have been used as fuel near Corfe and at Bovey . The Bracklesham beds (q.v..) are sometimes classed with the overlying Barton clay as Middle Bagshot . In the London basin the Barton beds are unknown . In Surrey and Berkshire the Bracklesham beds are from 20 to 50 ft. thick; in Alum Bay they are too ft., with beds of lignite in the lower portion; and about here they are sharply marked off from the Barton clay by a bed of conglomerate formed of flint pebbles . The Upper Bagshot beds, Barton sand and Barton clay, are from 140 to 200 ft. thick in the Isle of Wight . The Agglestone (or Haggerstone) rock and Puckstone rock, near Studland in Dorsetshire, are formed of large indurated masses of the Lower Bagshot beds that have resisted the weather; Creechbarrow near Corfe is another striking feature due to the same beds . Many of the sarsen stones or greywethers of S.E . England have been derived from Bagshot strata . See Memoirs of the Geological Survey (England) :—" Geology of the Isle of Wight," new edition (1889); " The Geology of London and Part of the Thames Valley," vol. i .

(1889) ; and ' The Geology of the

Country around Bournemouth " (1898) .