298 ME. T. M. EEADE AN ESTIMATE OF POST-GLACIAL TIME. 



the last being the alluvial flat. He corroborated Mr. Eeade's 

 statement as to the small change of level since the time of the 

 Eomans, but thought that in arguing with respect to the amount 

 of time, he was reckoning without his host ; for the valleys had reached 

 their negative gradient before the Roman period. There were no 

 links for the calculation of time for the formation of deposits older 

 than the Roman era. 



Dr. Evans had himself abstained from reducing geological time 

 to 3^ears, but he admired the Author's ingenuity. However, he had 

 left out of his calculation certain stages. There was no evidence as 

 to the time elapsed between the Boulder-clay and the base of these 

 deposits, and very little as to whether they were marine or alluvial. 

 If marine shells are absent these beds are probably alluvial and 

 comparatively modern. He contrasted the estimate of the time 

 required for their deposition with the short period allowed by some 

 recent authors for the interval between the Glacial epoch and the 

 present day. 



Mr. Clement Reid remarked that there was a verj- similar 

 succession in the deposits of the Humber. A rough calculation had 

 shown that the highest buried forest in that district may have been 

 submerged about 3000 years ago ; and the pile-dwelling at Ulrome 

 seemed to prove that it occurred before part of the Keolithic period. 

 He thought that the Author had overlooked the fact that when 

 the land was higher, denudation, and consequently deposition, would 

 be more rapid. This seemed to invalidate any calculations based on 

 the present rate of deposition of silt. He had found it impossible 

 to make any estimate of the time represented by the deposits below 

 the highest submerged forest. 



Mr. Whitaeee thought that Mr. Reade's post-glacial beds were 

 newer than the valley-gravels of the south-east of England. The 

 teims post-glacial and glacial have a different meaning in different 

 places ; some of the post-glacial drift of one district may be as old as 

 some of the glacial drift of another district ; thus southern post- 

 glacial drift may be as old as the Boulder-clay in the column. He 

 spoke of the rapid accumulation of alluvial marsh-clays and peat- 

 beds, as at Tilbury Docks. 



Mr. Topley pointed out that the beds under discussion, which 

 upon any view of the case represented a long period of time, were 

 later in date than those of the Cae-Gwyn Caves. 



Prof. Peestwich remarked that there was considerable corre- 

 spondence between Mr. Reade's section and that at Tilbury Dock, 

 but at the latter place the alluvial deposits were under 100 feet 

 thick, and rested, not on Boulder-cla}^, but on the latest of the valley 

 gravels, or true so-called post-glacial beds. 



The Aethoe scarcely expected that any one would fully agree 

 with him on the question of lapse of time. There had been some 

 misapprehension amongst the speakers, who had confined their 

 remarks mainly to the time occupied in the formation of what he 

 called the post-glacial deposits. But he had largely relied upon the 

 time occupied in the clearing out of enormous quantities of marine 



