,M47i^]; ' - PRESTWICH ON THE BAGSHOT SANDS. 381 



ham, Frimley and Hartford, similar as they are in general appearance, 

 can all he placed in their relative geological divisions with as much 

 certainty as though situated in the well-marked divisions of the cre- 

 taceous system. Instead of forming one mass of unfossiliferous sands, 

 with irregular subordinate beds of greeii sand and marls, the Bagshot 

 sands can be divided into three distinct and persistent divisions, seve- 

 rally characterized by pecuHar groups of organic remains and by dif- 

 ferences of hthological characters. .1 2lL J 



Lower Bagshot Sands. 



This division, which reposes* conformably on the London clay, con- 

 sists mainly of whitish and light yellow fine siliceous sands, frequently 

 micaceous and occasionally argillaceous, with a few seams of pebbles 

 and mere traces of organic remains. It varies in thickness from 100 

 to 150 feet. Thus in the well at Chobham Place (PL XIV. Comp. 

 Sec. fig. 10), after sinking through a portion of the upper sands 

 and the whole of the central green sand beds "5" (fig. 4. p. 384), 

 there was found about 100 feet of light-coloured sands "c,** and 

 below them the London clagf. At the Woking station 100 feet of 

 light-coloured sands were pierced through before reaching the London 

 clay, and if we then follow these sands, from the station to Golds- 

 worthy Hill (fig. 3. p. 382), where the outcrop of the central green 

 sands *'c" is very distinct, we shall have a total thickness of about 

 130 feet to this lower division. Again, at Knap Hill, at a short di- 

 stance from the outcrop of the central green sands, the borings passed 

 through 100 feet of light-coloured sands before arriving at the London 

 clay. At St. George's Hill near Weybridge, the sands may be traced 

 from the London clay at the base of the hill to the outcrop of the 

 green sands about halfway up it, a thickness of about 130 feet. At 

 Shapley Heath, adjoining the Winchfield station, the green sand 

 beds are seen resting upon the lower sands, which may be followed 

 down the hill to the London clay, giving an estimated thickness of 

 about 100 feet (see PL XIV. Comp. Sec. fig. 9). 



Numerous other wells and many small road-side sections occur in 

 the lower sands, but the bulk of them are only of a very partial and 

 limited character ; still they are important, inasmuch as they show 

 the uniformity of structure of this division of the Bagshot sands. 

 Thus in Virginia Water Park, around Woking, at Claremont, Cob- 

 ham, Ripley, Ascot, and wherever else exposed, these lower sands 

 exhibit no traces of green sands. Thin and finely laminated sub- 

 ordinate and irregular beds of whitish, light yellow, brown and 

 liver-coloured fine clays with sands are of not uncommon occur- 



* This was well exhibited in the railway cutting through St. George's Hill. 

 At the end, near the Walton station, I traced the London clay for a distance of 

 several hundred feet passing conformably below the lower Bagshot sands. Again 

 near Egham and elsewhere, as mentioned by Mr. Warburton. 



t The well was continued through the London clay 400 feet ; then through 

 about 50 feet of mottled clays and sand, and into the chalk to a depth of 150 feet, 

 making a total depth of about 800 feet. These measures were given rae from 

 recollection by an old man who had worked at the well, and are therefore liable 

 to error ; I however believe them to be tolerably exact. 



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