WESTLETON BEDS TO THOSE OF NORFOLK, ETC. 121 



These are lost in later stages, owing to frequent reconstruction, but 

 we can then follow by levels. 



In 1847 * I showed that in the neighbourhood of London there 

 were hill-gravels as distinct from valley-gravels, but I was not then 

 in possession of any clue whereby to fix their separate age. Subse- 

 quent observations, especially aided by the cuttings on the Great 

 Eastern Railway then in course of construction, enabled me to 

 follow the Pre-Glacial Beds of Suffolk in their inland range, and to 

 recognize their higher position in relation to the Drifts of the 

 Thames Yalley. 



In my paper of ^ 871 on the Westleton Beds f I briefly alluded 

 to their extension into the Thames Yalley area, but reserved the 

 details for subsequent description. Other occupations and the need 

 for verification of some of my early observations led to a loug delay 

 in publication, though in 1881 1 I gave a short preliminary notice of 

 some of the hill-drifts in the London Basin — such as those at High- 

 beech, Barnet, Southgate, Hertford, Hatfield, South Mimms, St. 

 Albans, Tiler's Hill, Horsington, and Bowsey Hill § — which are 

 capped by Drift Beds of Westleton age. I now purpose giving these 

 in detail, and I only regret that owing to the lapse of time many of 

 the sections I have to describe are no longer visible. The delay, 

 however, gives me the advantage of the observations recorded by 

 other geologists, and especially by Mr. Whitaker and other officers 

 of the Geological Survey, and also enables me to avail myself 

 of the heights and contours given in the last published sheets of 

 the 1-inch Ordnance Survey, so indispensable in an inquiry of this 

 description, and for which I had previously to depend on the obser- 

 vations I had made with an aneroid barometer ||. 



In 1804, Mr. Whitaker, in his account of the Post-Pliocene 

 Series ^ of parts of Middlesex, Hertfordshire, Buckinghamshire, 

 Berkshire, and Surrey, alludes to the occurrence of a " gravel wholly 

 or for the greater part made up of flint pebbles " on the tops of vari- 

 ous hills in Hertfordshire and Buckinghamshire. 



In 1877 he stated that there were two gravels in East Essex**, 



* ' The Ground Beneath us,' }3. 30. 



t Quart. Journ. Geol. Soc. vol. xxvii. p. 477. 



I Keports Brit. Assoc, p. 420. I was not then acquainted with Mr. Wbita- 

 ker's latest Memoir. 



§ Other hills were named, but these relate to the Southern Drift, which I 

 now take separately. 



II I regret also that I find it impossible to revisit, as I had intended, the 

 many localities described, in order to check and revise my early observatious, 

 the greater number of which were made before my views were matured. Conse- 

 quently, there may be inaccuracies which have escaped me, or analogies which 

 I may have overlooked. I could also have wished to have given greater 

 certainty to the percentage values of the Westleton and Southern Drifts — a 

 plan which only occurred to me after much of the work had been done. I fear 

 I may have overestimated the relative proportions of some of the esscMitial 

 constituent materials, but not to such an extent as to vitiate the general argu- 

 ment, while the facts, I trust, are recorded with sullicent accuracy to justify the 

 conclusions at which I have arrived. 



% Mem. Geol. Survey, Expl. Siieet 7, p. (J9 (18G4). 



** " On the Geology of the Eastern End of Essex (Walton-on-Xaze and Har- 

 wich)," Expl. of Sheet 48 S.E. p. IG. 



k2 



