294 THE STORY OF THE EARTH AND MAN. 



necessarily smaller tlian the outer ; nor for tlie further 

 fact that the older cone belongs to a distinct time 

 (the pluvial age already referred to)_, when the rainfall 

 was much larger, and the transporting power of the 

 torrent great in proportion. Making allowance for 

 these conditions, the age of the newer cone, that 

 holding human remains, falls between 4000 and 5000 

 years. The peat bed of Abbeville, in the north of 

 France, has grown at the rate of one and a half to 

 two inches in a century. Being twenty-six feet in 

 thickness, the time occupied in its growth must have 

 amounted to 20,000 years; and yet it is probably 

 newer than some of the gravels on the same river 

 containing flint implements. But the composition of 

 the Abbeville peat shows that it is a forest peat, and 

 the erect stems preserved in it prove that in the first 

 instance it must have grown at the rate of about three 

 feet in a century, and after the destruction of the 

 forest its rate of increase down to the present time 

 diminished rapidly almost to nothing. Its age is 

 thus reduced to perhaps less than 4000 years. In 

 1865 I had an opportunity to examine the now 

 celebrated gravels of St. Acheul, on the Somme, by 

 some supposed to go back to a very ancient period. 

 With the papers of Prestwich and other able obser- 

 vers in my hand, I could conclude merely that the 

 undisturbed gravels were older than the Roman 

 period, but how much older only detailed topographical 

 surveys could prove ; and that taking into account 

 the probabilities of a different level of the land, a 



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