564 PEOCEEBINGS OF THE GEOLOGICAL SOCIETY. [JuTlG 20, 



The surface of the high-level gravels, and of the brick-earth which 

 often covers them, appears to have been affected by the same fur- 

 rowing action which has operated upon the surfaces of older beds. 

 They are also enveloped by the true warp, which seems to have been 

 formed chiefly by severe winter frosts, and by other siibaerial causes, 

 before the last depression of the land ; for, as I have shown, the warp 

 is covered by the alluvial deposits. In the valley of the Stour, about 

 Sudbury, in Suffolk, the valley-gravels are to be seen furrowed by 

 trail from the higher grounds. The flints from the Boulder-clay in 

 the trail are there coarser than those in the gravel which contains 

 the furrows. An excellent section of the trail is also to be seen in 

 the Ilford Brick-pits. 



We have, then, data for fixing the period of the formation of the 

 warp over the surface left, in all probability, in a bare condition by 

 a preceding general denudation. It was subsequent to the period 

 when the ElejpTias primigenius lived in company with E. antiquiis, and 

 when chipped implements were used ; for the gravels which con- 

 tain those associated relics have been affected by the denudation 

 which preceded the formation of the warp. But it was previous 

 to the growth of the newest submarine forests, which occupied the 

 surface before the last depression of the land. It appears to have 

 been the period which, before the glaciers of Scotland finally disap- 

 peared, left the moraines described by Mr. Jamieson as having been 

 formed anteriorly to the deposition of the Carse clay*; for there seems 

 little doubt that that clay is the equivalent of the marine silt with 

 Scrohicularice which covers our English submarine forests, and that 

 the elevation which Mr. Jamieson tells us must have been so general 

 over a large part of the western seabord of Europe f was followed 

 by a depression, if not quite so general, at least very extensive. 



Upon reviewing the changes which have been indicated by the 

 phenomena discussed in the present paper, we have disclosed, 

 in the first instance, a condition of the surface when the general 

 features of the landscape were the same as at present, during which 

 the great mammalian fauna flourished contemporaneously with the 

 fabricators of the chipped flints. 



We have, subsequently, though perhaps not in immediate 

 sequence, a period of extensive denudation, indicated by the furrows 

 filled with materials from the higher grounds, which have travelled 

 in a plastic state, and which I have called '' trail." This denuda- 

 tion brought the surface almost exactly to its present form. The 

 period of the formation of the warp succeeded, in which the winter 

 frosts seem to have been more severe than at the present time. 



It was either during this period, or shortly afterwards, that the 

 submarine forests flourished. A submergence of moderate amount, 

 measured by a few tens of feet, next followed, and the Scrobicu- 

 laria-mud was deposited over the lowest forest-grounds. The sea 

 was then depressed again, and the recent period commenced. 



The changes of form in the present surface which have taken 

 place since that time may, I believe, be easily recognized, since they 

 ^ Quart. Journ. Gleol. Soc. vol. xxi, p. 173. t Ibid. p. 180. 



