70 DURATION OF THE ALLUVIAL PERIOD 



another, and this drift is, as I have before explained, 

 a detrital bed requiring but a short time for its 

 formation. 



If then the lapse of time since the formation of 

 this detrital bed were known, we might hope to arrive 

 at some conception of the approximate date of the 

 Submergence, and of the time which separates 

 Recent from Palaeolithic Man. In this country 

 two scales may possibly prove available the one is 

 that afforded by the Alluvial beds of such valleys as 

 those of the Thames and others in the south of 

 England ; and the other by the extent of denudation 

 or wearing back of the Rubble-drift of the " Head " 

 that has taken place 'on the coast since it was formed. 

 With respect to the Alluvial deposits, though their 

 structure and organic remains indicate their recent 

 origin and comparatively j*apid growth, their thick- 

 ness is so variable, and the rate of growth of the 

 peat-beds so uncertain, that a wide range must be 

 allowed. We know that within Neolithic times there 

 has been in places a growth of ten to eighty feet of 

 these deposits. The skeleton of recent Man at Tilbury 

 was found under thirty-four feet of clay and peat. In 

 the Valley of the Somme, Gallo-Roman remains have 

 been found under a depth of eighteen feet of peat. As 

 however the thickness of these beds rarely exceeds 

 about 100 feet, and is generally limited to twenty to 

 forty feet, it is manifest, although we cannot define the 

 period with exactness, that the age of the Alluvial 

 beds is to be measured, not by tens of thousands, but 

 by tens of hundreds of years. 



