A HISTORY OF SURREY 



diles and fish, together with marine shells numerous both in individuals 

 and in species, and plant- remains ; and these, as already mentioned, 

 indicate a warm, almost sub-tropical temperature. 



Where the outcrop of the London Clay enters the county on the 

 west, near Farnham Park, it is comparatively narrow from a half to 

 three-quarters of a mile in width owing to the steep northerly dip, 

 but it expands as the dip decreases, until near Leatherhead it attains a 

 width of about three miles. East of this locality, owing to the upward 

 shelving of the south-eastern margin of the London Basin the strike of 

 the beds swings northward, and the London Clay, no longer covered by 

 the Bagshot Beds (except by a few small outliers), lies exposed in a 

 wide sheet extending to the banks of the Thames and occupying all the 

 north-eastern part of the county around the suburbs of London, save 

 the little strip previously described where the underlying strata come to 

 the surface. The Clay also stretches along the Thames Valley at the 

 northern border of the county to Chertsey and Egham, though usually 

 covered in this quarter by the Recent Valley-deposits presently to be 

 discussed. Wherever exposed at the surface it forms a heavy cold 

 clay-land, but in many parts of its outcrop this character is modified by 

 the presence of thin ' superficial ' accumulations of gravel, loam and 

 brick-earth of Post-Tertiary or Recent age. 



BAGSHOT BEDS 



After the long period of depression indicated by the London Clay, 

 the pendulum of change once more swung slowly back, and a gradual 

 re-elevation set in which brought shallow water conditions again into 

 our area. This change is indicated by the character of the beds by 

 which the London Clay is overspread, which consist of a thick mass of 

 sand and pebbly beds, with a subordinate clayey portion, known collec- 

 tively as the Bagshot Beds. Fossils are extremely rare throughout this 

 series in Surrey, but the few that have been found indicate that the 

 deposits are of marine origin. The equivalent beds in the Hampshire 

 Basin are, however, in their lower portion, partly fluviatile and estuarine, 

 so that we seem, as in case of the Woolwich and Reading Beds, to have 

 evidence of the existence of a river flowing from west to east during the 

 accumulation of the series. 



Much has been written respecting the subdivision and correlation 

 of the Bagshot Beds, 1 but for our present purpose it is sufficient to note 

 that in Surrey a threefold division, based on the composition of the 

 strata, is possible. 3 Of these, the lowest (Lower Bagshot Beds) consists 

 mainly of fine whitish or yellowish sand, often micaceous, sometimes 

 slightly laminated or intermixed with clay, and occasionally containing 



1 See J. S. Gardner, Geol. Mag. 2, dec. vol. vi. (1879) p. 151, and Quart. Journ. Geol. 

 Sec., xxxv. p. 210 ; Rev. A. Irving, Quart. Journ. Geol. Sec., vol. xlviii. p. 485, and several 

 other papers ; H. W. Monckton, Quart. Journ. Geol. Sac., xxxix. p. 352, and xlviii. p. 48, etc. ; 

 Monckton and Herries, ibid. xlii. p. 415 ; H. G. Lyons, ibid. vol. xlv. p. 633 ; etc., etc. 



It is now generally agreed that the so-called Upper Bagshot Beds of Surrey are not 

 strictly equivalent to the Upper Bagshots of the Hampshire Basin. 



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