1847.] PRESTWICH ON THE BAGSHOT SANDS. 383 



^'': . feet. 



'!' ftf 8. Grey clay with traces of lignite I 



4. Green sand; upper part light-coloured and clayey, the lower part pure and dark- 



coloured. Numerous teeth and bones of fishes and turtles, casts of Turritella sulci- 

 fera and Vcnericurdia planicosta, &c. (see List, p. 390) l6 



5. Compact lignite 1 



6. Light- coloured compact sandy clay, passing downwards into dark grey clay. The 



upper part is irregularly pierced with green sand-tubes 6 



7. Light and dark brown and liver-coloured very compact foliated clays, with traces of 



vegetable impressions 8 



c. Lower Bagshot Sands. 



Light yellow sUiceous sands with irregular light- coloured argillaceous beds. Traces of 

 vegetable impressions 130 



d. London Clay (upper part of). 



X Interval of three miles, f Interval of quarter of a mile. 

 In both these spaces the strata are continuous. 

 Portions of strata proved. 



The section at Shapley Heath, adjoinmg the Winchfield station, is 

 almost an exact counterpart of this one. 



Middle Bagshot Sands. 



Overlying the lower sands are a few heds of white, yellow, sulphur- 

 coloured, hrown, liver and cream-coloured laminated clays, and one 

 or two beds of green sands. Their thickness altogether does not ex- 

 ceed from forty to sixty feet ; they nevertheless form a division, not 

 only of distinct mineral character, but also of extremely persistent 

 range and structure. The lowest part usually consists of light- 

 coloured and dark brown, very compact or impalpable foliated clays, 

 frequently laminated with light-coloured sand, and occasionally with 

 subordinate beds of lignite (*'6. 6 to 7," fig. 3). These clays are 

 most extensively developed around Addlestone and Chertsey, where 

 they attain a thickness of ten to twenty feet. In their range west- 

 ward they gradually diminish to a thickness of five feet at Shapley 

 Heath (PI. XIV. Comp. Sec. 9 and 10). 



Above these clays is a thick stratum of green sand, generally very 

 pure and of a dark bottle-green colour, and maintaining a tolerably 

 uniform thickness of about twelve to twenty feet (*'5. 4," fig. 3, and 

 " b. 2," fig. 4). It is occasionally fossiliferous, but of this hereafter. 

 To this main bed succeed a few layers of more variable and impure 

 green sands, frequently exhibiting false stratification, and of brown, 

 yellow, and light greenish clays, usually, but not always, laminated. 

 Intercalated with these green sands are occasional layers of large and 

 small rolled flint pebbles. 



This division forms an excellent geological horizon, dividing the 

 lower from the upper Bagshot sands ; and its outcrop may easily be 

 traced on the sides of the hills by the line of small springs to which it 

 gives rise, or by the frequent presence of marsh- and water-plants. 

 ^Thus from Goldsworthy it may be followed through Worplesdon to 

 above Normandy ; is again visible east of Crookham, near Crondall ; 

 thence to Hartford Bridge, Shapley Heath, round to Finchamp stead, 

 Swinley, branching off to Bagshot, passing thence north of Chobham, 

 by Knowles Hill, to the south of Sunninghill and Ascot*. 



In the valleys its presence is indicated by their greater fertility and 

 the general occurrence of small water-courses. This has led to the 



* Its exact course can only be given on a map. These are merely a few of the 

 places where it is visible. 



