OF THE BAGSHOT BEDS OP THE LONDON BASIN. 181 



gravel-capping, to which the hill owes its preservation. The ridge 

 of this hill is traversed by the Whitway, on the west of which is 

 Highclere Park. 



Eestjlts. 



When it is observed that the Upper-Bagshot outlier is about 18 

 miles due west of those places (Shapley Heath and Bramshill) which 

 mark the extreme westerly limit of previous records of beds of that 

 group, the importance of their identification becomes apparent. It 

 appears that the marine estuary, in which the Upper Sands were 

 deposited, extended over the region of Chertsey and Sandhurst for 

 miles in a long narrow arm to the west, partly along what is now 

 the valley of the Kennet and the Enbourne*, and it seems to offer 

 support to the view, which I have long held on general grounds, of 

 the great antiquity of this arterial line of drainage of southern 

 England. In the light of such evidence we are perhaps justified in 

 dating back its existence at least to Eocene times, thus giving a 

 high antiquity to the great Kennet-Thames line of drainage, com- 

 pared with which the drainage of the Isis basin into the Lower 

 Thames, by the cutting of the Pangbourne gorge across the strike 

 of the Chalk, may almost be spoken of as a recent event in t.he 

 physical history of the South of England. 



Another interesting point is the sharp dip of the Chalk on the 

 north of the Kingsclere axis of elevation (equalling that of the 

 Hog's Back), while the great attenuation of the London Clay to 

 the west, as shown by a comparison of its thickness at Highclere 

 with its thickness at Aldershot and Ash, seems to suggest a partial 

 elevation of the Kingsclere axis during the London-Clay period. 

 On the other hand, the pretty constant thickness of the "Woolwich 

 and Reading Beds seems to forbid the assignment of an earlier 

 period than the London Clay to the Kingsclere upheaval. 



Again, the high dip of the Chalk at Highclere (30° IS .), as com- 

 pared with the more moderate dip of the Bagshot Beds (10° N.), as 

 shown in our section (p. 179), affords evidence of very considerable 

 pre-Bagshot elevation of the Kingsclere axist. Whether the whole 

 of the Bagshot series was equally affected by later movements is a 

 question which, with our present data, cannot perhaps be answered; 

 and with the results of Lieut. Lyons's work in the Aldershot district :|: 

 before us, we seem as much in the dark as ever as to the extent 

 and duration of any communication between the London and 

 Hampshire Basins, after the close of the period represented by the 

 Woolwich and Eeading Beds. Perhaps the work of the officers of 

 the Survey in Hampshire may bring to light some evidence of atten- 

 uation or overlap, which may go some way towards settling this 



* This obviously necessitates a reconsideration of the stratigraphy of the 

 intermediate country, and more especially that of the Bagshot Beds of the 

 district about Banghurst and Eamsdell. 



t See Barrois, 'Eecherches sur le terrain cr^tace superieur/ 1876, pp. 114, 

 115; also fig. 8 of the plate appended to that monograph. 



J Quart. Journ. Greol. Soe. vol. xliii. August 1887, pp. 432-441. 



