CHAPTER IX. 



IIAMPSTEAI) HILL ITS SUBSTRUCTURE. 



Regarding Hampstead Hill as standing on a base lOO feet 

 above Ordnance Datum, its substructure or foundations, so to 

 speak, for i,ooo feet in depth is a composite one, as is shown by 

 the vertical section (Plate IX.). There is first the lower portion of 

 the already-described London Clay with Its basement bed, 400 

 feet, then the Woolwich and Reading Beds below of 60 feet, with 

 the underlying Thanet Sands of 30 feet thickness. Below all 

 these beds lies the great Chalk formation, having here a total 

 thickness of about 650 feet, but divisible into the Upper Chalk 

 with flints, 250 feet ; the Lower Chalk without flints, 340 feet ; 

 and the Chalk Marl, 60 feet. At the base of the Chalk series 

 there is a comparatively thin bed of 20 feet, called the Upper 

 Greensand, and this rests upon the Gault Clay, which makes up 

 the remainder of the 1,000 feet of strata underlying the base 

 of Hampstead Hill. 



The Woolwich and Reading Beds are very variable, but yet 

 display in the western, or Reading, area a decided difference of 

 character from that of the beds in the eastern, or Woolwich, area. 

 This difference is sufficiently distinct and important, since it 

 indicates a geographical difference of conditions of deposition, to 

 justify the use of the two names, Woolwich and Reading, for the 

 designation of the formation as a whole. The fossils of this 



