476 On the Agricultural Geology of England and Wales. 



denudation, and broke the continuity of the eocene tertiaries, 

 separating them into the London and Hampshire districts, is 

 placed by Ehe de Beaumont in the erratic period, because of its 

 east and west strike. The direction of Hues of disturbance, un- 

 supported by other evidence, cannot be deemed conclusive of the 

 periods when the disturbance took place, since it has been ascer- 

 tained that they have in many instances been repeated along the 

 same line at different geological epochs. There is, however, 

 enough in the circumstances which have been mentioned to render 

 the relations of this flint gravel to the east and Avest line of dis- 

 turbance — to the gravel beds on the high grounds north of the 

 Thames, and to the fluviatile deposits in the valley of the 

 Thames, containing bones of elephants and other large mammals 

 ■ — an attractive subject of investigation to geologists: it is still 

 involved in much obscurity, and can only be worked out effec- 

 tually by mapping the surface variations on both sides of the 

 Thames.* 



Whatever the age of these deposits may prove to be, the fact of 

 importance to agricultural geology is that large areas are covered, 

 in the southern counties, with beds of gravel so deep as to exercise 

 a great influence on the soil, which have no place on geological 

 maps as at present constructed. 



Districts most free from Erratic Deposits. — We have now ex- 

 tended our survey of the erratic deposits over the whole of Eng- 

 land and Wales, with as much detail as our limits, and, we may 

 add, the present state of geological knowledge respecting these 

 deposits will permit. The result is, that the only large districts 

 over which the submergence of that period can, by any possibility, 

 be supposed not to have extended are the following : — The more 

 elevated portions of the Cumbrian, Cambrian, and Penine chains, 

 which exceed 1400 or 1500 feet in height — tracts which have but 

 little agricultural value — the county of Cornwall, with parts of 

 Devon ; the more elevated portions of the oolitic ridges, particu- 

 larly in the south, near the head waters of the Thames and its 

 tributaries ; and the Weald of Kent, Sussex, and Surrey. With 

 respect to the last, which is considered by some to have enjoyed 

 the same immunity from invasion by the erratic sea which is 

 claimed for it from foreign conquest in the old rhyme — 



" The winding vale of Holmsdale 

 Was never won and never shall," 



it may be remarked that, though generally free from extraneous 



! * Since this passage was written, papers, not yet published, on these south-eastern 

 deposits, have been read before the Geological Society, by Sir R. Murchison, Mr. 

 Austen, and Mr. Prestwich, which, from their conflicting views, prove how much the 

 subject still requires investigation. 



