BAGSHOT SERIES. 33 



zircon, rutile and tourmaline. In the sand at Weybridge, 

 Hudleston noted that the bulk of the grains were quartz with 

 a few chips of flint or chert, glauconite, and oxide of iron. 



BBACKLESHAM BEDS. 



This formation is divisible into three parts ; the lower consists 

 of clay, usually laminated and of a lilac or purplish tinge, though 

 sometimes brown; in the middle is a highly glauconitic sandy 

 bed, often of a deep pistachio green and fossiliferous ; the upper 

 consists of sand, loam and clay with an impersistent pebble-bed 

 at the base. 



The full thickness may be as much as 100 ft. at St. George's 

 Hill, but is less further west. The figures are very variable, as 

 the lower clays usually rest in basin-like hollows cut in the 

 Bagshot Sand and the pebble-bed at the base of the Barton 

 may cut out varying amounts of the upper part. 



Fossils have not been definitely recorded from the area here 

 dealt with, although casts of bivalves have been found; but 

 there are several localities to the west and south-west where a 

 considerable number of mollusca and a few fish teeth and bones 

 of turtles occur. 



The characteristic shells are the screw-shell Turritella sulcifera 

 Deshayes, oysters (Ostrea flabellula Lamarck), and the large, 

 thick, oval bivalve Venericardia planicosta Lamarck, marked with 

 prominent radial ribs. The disc -like foraminifer Nummulites 

 Icevigatus (Brug.) is also typical of beds of this age. These forms 

 indicate deposition in a- shallow sea in a warm climate. 



BARTON BEDS. 



The Barton Beds consist essentially of yellow sands, usually 

 with a pebble-bed at the base. They are not indicated on the 

 map, but an important outlier, showing a thickness of at least 

 50 ft., occurs on St. George's Hill. The sands were recognised 

 by H. B. Woodward and by Mr. Monckton as belonging to this 

 division and have now been studied in detail. 1 They are shown 

 on the new Windsor Map (Sheet No. 269). Outliers of the basal 

 pebble-bed have been detected near our western margin, but it is 

 apparently absent at St. George's Hill. It is well developed at 

 Stanner's Hill,' one mile west of Ottershaw, and contains pebbles 

 of Greensand chert as well as flint; as this chert is not known 

 from older Tertiary beds the occurence serves to indicate the 

 date at which denudation of the W^eald first uncovered the 

 Lower Greensand. 2 



1 ' Geology of Windsor and Chertsey ' (Mem. Geol. Surv.}, 1915, pp. 51-58. 



2 Op. cit,, pp. 53, 55. 



B 4 



