42 ME. C. J. GILBERT OX DEPOSITS OF HIGH-LEVEL [vol. lxXV„ 



continuous sheet from Little Heath as far, afc any rate, as Potten. 

 End, about half a mile to the north; also, east and west from 

 Little Potten End across Berkhamsted Common, for a distance of 

 at least 1^ miles. The last-named locality is also covered with 

 old gravel- pits. 



Jt is believed that the presence of stratified deposits of sand and 

 gravels of this character at so high an altitude has not hitherto 

 been recorded on the north side of the Thames Valley. 



Over a considerable area of Northchurch Common, about 2k miles 

 north-west of the Berkhamsted deposits, there is an enormous 

 quantity of pebbles, precisely similar in character, and many of 

 them very big, together with worn and unworn flints. These 

 have been worked for many years, but nowhere to any great depth.. 

 Whether they are underlain by the stratified gravels in situ has 

 not yet been determined; but in any case it seems clear that the)' 

 cannot have been derived from the Berkhamsted beds on the south- 

 east, and, even if their presence be due to glacial or other agencies, 

 the beds must originally have extended to a considerable distance 

 from the Berkhamsted deposits. 



The Age of the Loamy Saxd- akd Gbaa'el-Beds. 



Pending the discovery of evidence which will finally settle the 

 age of these beds, the following comments are offered : — 



That they are not Reading Beds is proved by the fact that they contain 

 well-rounded pebbles of puddingstone, of which several specimens 

 were obtained from different parts of the pebble-beds. The big* 

 waterworn and semi-waterworn flints, and the great quantities of white 

 quartz-pebbles which form so large a proportion of the beds, also- 

 differentiate them from the typical Reading deposits. 



Having then arrived at the fact that they are not of Reading age, we can 

 take a considerable leap forward. The Little Heath beds are at the 

 top and on the upper flanks of the hills, where not only the Reading 

 Beds but the London Clay must have originally been deposited ; 

 indeed, there are fragments of the Reading clays and an abundance of 

 Reading pebbles in every direction. 



Now, wherever the base of these Little Heath deposits has been reached, 

 they are invariably found to rest directly upon the Chalk without 

 the slightest evidence of intervening Reading Beds. It is obvious 

 therefore — 



(a) That the London Clay and the Reading Beds had alike been denuded 



before their deposition. 



(b) That there is, consequently, a great unconformity between them and 



the Eocene beds, and 



(c) That they must be later than the Eocene Beds. They are also Pre- 



Glacial. 



Gexeeal CONCLUSIONS. 



These deposits differ from other kindred deposits north of the- 

 Thames, in that they rest directly upon the Chalk. They are found 

 up to at least 560 feet above Ordnance Datum, and extend with 

 practical continuity for at least 1^ miles in length, and in one- 



