BAGSHOT BEDS

This article appears in Volume V03, Page 207 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: AUD-BAI

BAGSHOT BEDS , in geology, a

series

SERIES (a Latin word from serere, to join)

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

HAMPSHIRE (or COUNTY OF SOUTHAMPTON, abbreviated HANTS)

basins (England), and derive their name from Bagshot Heath in Surrey; but they are also well developed in

Hampshire

HAMPSHIRE (or COUNTY OF SOUTHAMPTON, abbreviated HANTS)

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

PALE (through Fr. pal, from Lat. palms, a stake, for paglus, from the stem pag- of pangere, to fix; " pole " is from the same original source)

-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

SHARP,
GRANVILLE
- GRANVILLE
- GRANVILLE, GRANVILLE
- GRANVILLE, JOHN
  CARTERET
  - CARTERET, SIR GEORGE (c. 1610-1680)
  , EARL (1690-1763)
(1735-1813)
SHARP, JAMES (1618-1679)
SHARP, JOHN (1645-1714)
SHARP, RICHARD (1759-1835)
SHARP, WILLIAM (1749-1824)
SHARP, WILLIAM (1856-1905)

line can be

drawn

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

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

SERIES (a Latin word from serere, to join)

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

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).

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