STRATA OF THE LONDON BASIN. 79 



of sand and sandstone, with intercalations of marl 

 and clay. These strata cover the London clay 

 from near Finchley on the north to Hampstead- 

 heath, and form part of the eminence on which 

 Highgate is situated. The Bagshot sands appear 

 at Egham, and extend, with some interruptions, to 

 near Guildford ; and from the vicinity of Kingston 

 to seven miles west of Bagshot, spreading over 

 part of Windsor forest. Several eminences in 

 Surrey are capped by this sand ; at Tucksbury- 

 hill, north of Farnham, it occurs at an elevation 

 of 500 feet.* From the siliceous nature of the 

 soil formed by these deposits, the districts in 

 which they occur are exceedingly sterile, sup- 

 porting only a covering of heath and furze ; hence 

 the numerous uncultivated wastes within a short 

 distance of London. But where the clays rise to 

 the surface, verdant spots appear in the midst of 

 these desolate tracts. The situation of these 

 argillaceous beds is indicated by the oozing of 

 water, and the growth of rushes in the bottoms of 

 the shallow valleys that traverse the sandy plains, 

 and which are often covered with peat. Some of 

 the Bagshot sandstone is remarkable for its struc- 

 ture, which partakes more of the character of a 

 peculiar crystallization than of a mere aggregation 



* Brayley's History of the County of Surrey, vol. i. p. 131. 



