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18 know the minimum extent of the change of level; but its full amount has to be ascertained from other localities.

This difficulty has seemed of far greater importance than it really is, and some geologists have suggested that at this period of maximum elevation, England stood several hundred feet higher above the sea than it does now. I doubt if such can have been the case. Granting that the sea may have been some 300 miles away from Tilbury, measured along the course of the winding river, this 300 miles would need a very small fall per mile, probably not more than an inch or two. The Thames was rapidly growing in volume, from the access of tributaries, and was therefore flowing in a deeper and wider channel, which was cut through soft alluvial strata; it therefore required less and less fall per mile. Long before it reached the Dogger it probably flowed into the Rhine, then containing an enormous volume of water and draining twice its present catchment area.

The clean gravel and sand which occupy the lower part of the ancient channel at Tilbury require to be more closely examined, for it is not clear that they are, as supposed, of fluviatile origin; they may quite well be estuarine. In the sand Mr Spurrell found the freshwater shells Bythinia and Succinea, and in it was also found the human skeleton described by Owen; but, according to Mr Spurrell, on the surface