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 GEOLOGY Ouse, and it is not until after the Lea leaves the county that there is any considerable sheet of alluvium in its valley. Alluvium is a silty deposit of sandy clay or peaty mud, in which there may be seams of gravel. It contains recent land and freshwater shells, sometimes bones of existing animals, and occasionally Neolithic flint implements. These are fairly common on both sides of the Lea from its source at Leagrave to its outflow in the Thames. Many such implements have been found in the county, but as they do not occur in regularly-stratified deposits, usually being found on the surface of the ground or just under the sur- face-soil, and occasionally in alluvium, their consideration rightly belongs to the domain of Pre-historic Archaeology. EARLY NOTICES OF BEDFORDSHIRE GEOLOGY The earliest notices of the geology of Bedfordshire relate to strata of economic importance, to petrifying earth, and to mineral springs. The soil of the county was mentioned so early as 1615; ' petrifying earth at ' Aspley-Gowiz ' (Guise) near Woburn claimed much attention from the year 1660, 2 and the fullers' earth of Woburn from the year 1662. 3 In 1680 * it was stated that a gold mine had been discovered at ' Pollux Hill ' near Silsoe, and the statement was repeatedly copied, even being mentioned as a fact in Calvert's Gold Rocks of Great Britain and Ireland (1853). Although the Society of Mines Royal seized the mine and granted a lease of it, the ' gold ' was merely flakes of mica in drifted stones occurring in a bed of gravel. On the Ordnance Map (old series) ' Gold Mine ' marks the position north-east of Pollox Hill in a field which is still called Gold Close. A petrifying spring at Barton was first mentioned in 1738 ; s mineral springs generally were frequently alluded to from the year 1808, 6 some dozen localities for them being mentioned in various works ; and ferru- ginous water at Priestley Bog near Woburn was analyzed by Sir Humphrey Davy in 181 3.' It is probably of the same origin as the mineral water of Flitwick Moor and somewhat similar in composition. The Totternhoe Stone seems to have been first described in 1820 ; 8 and although Professor Henslow called attention to the value of phosphatic nodules for manure in 1845, the ' coprolites ' of Bedfordshire do not appear to have been noticed until 1866. 9 1 John Speed's [Description of England ami Wales}: ' Bedfordshire.' (Without title-page or pagination.) 2 Childrey's Britannia Baconica, p. 86. 3 Fuller's History of the Worthies of England, p. 114. under the above date. See also p. 109, in which he gives a list of unauthenticated gold localities.) 6 Atlas Geograpkicus, i. 150. 7 Elements of Agricultural Chemistry, p. 291. 8 E. Hanmer, ' Letter describing the Totternhoe Stone,' Ann. Philos. xvi. 59. (It was in this year that William Smith published his Geological Map of Bedfordshire, the earliest geological map of the county.) 8 Rev. P. B. Brodie, ' On a Deposit of Phosphatic Nodules at Sandy in Bedfordshire ' ; Geol. Mag. iii. 153-5. (With analysis by Dr. Voelcker.) 31
 * Abbot's Essay on Metallic Works, p. 203. (Not seen ; referred to in Calvert's Gold Rocks, p. ioi,
 * Batchelor's Agriculture of the County of Bedford, p. 15.