ITS STRUCTURE. 21 



Bagshot Sands which form the uppermost part of the hill, in- 

 cluding the area on which the higher portion of the town of 

 Hampstead stands. All the higher levels of the Heath are 

 consequently on the sand, the sterility of which was the cause 

 of so large a tract of land near the metropolis remaining un- 

 enclosed. Hence it is that the existence of the Heath and 

 its appropriation to the people for ever as a public recreation 

 ground, is the direct result of there being here a patch of 

 the Bagshot Sands capping the London Clay forming the mass 

 of the hill. 



As the extreme elevation of the hill is 443 feet above 

 Ordnance Datum, the Bagshot Sands have here, consequently, 

 a maximum thickness of about 80 feet. The uppermost 

 beds of the London Clay, to the thickness of about 50 feet, 

 are sandy, becoming more so as the junction with the overlying 

 Bagshot beds is approached. There are therefore three more 

 or less distinct deposits: (i) the typical London Clay forming 

 the base and the great mass of the hill ; (2) the Upper 

 Sandy London Clay above, and (3) the sands of the Bagshot 

 Sands formation capping these and forming the summit of the 

 hill. 



This simple structure of Hampstead Hill will be at once 

 seen from the diagram, Plate VH,, representing an ideal section 

 through the hill and across the valley of the Thames from the 

 Chalk Country of Bucks and Hertfordshire on the north to the 

 Chalk Downs of Surrey on the south. 



