THE DATE OF THE GLACIAL PERIOD. 355 



found in this, but it doubtless corresponds in age with the 

 high-level gravels in the valley of the Somme, in which 

 the remains of man and the mammoth, together with 

 other extinct animals, have been found. 



We do not see, however, that any very definite calcu- 

 lation can be made concerning the time required for its 

 deposition. Lyell was inclined to consider it ten times as 

 old as the modern delta, simply upon the ground of its 

 being ten times as large. On Morlot's estimate of the age 

 of the modern delta, therefore, the retreat of the ice whose 

 melting torrents deposited the upper delta would be fixed 

 at 100,000 years ago, and upon Dr. Andrews's calculation, 

 at about 20,000. 



But it is evident that the problem is not one of simple 

 multiplication. The floods of water which accompanied 

 the melting back of the ice from the upper portions of 

 this valley must have been immensely larger than those 

 of the present streams, and their transporting power im- 

 mensely greater still. Hence we do not see that any con- 

 clusions can be drawn from the deltas of the Tiniere to 

 give countenance to extreme views concerning the date of 

 the close of the Glacial period.* 



In the valley of the Somme the chronological data 

 relating to the Glacial period, and indicating a great an- 

 tiquity for man, have been thought to be more distinct 

 than anywhere else in Europe. As already stated, it is 

 the prevalent opinion that since man first entered the 

 valley, in connection with the mammoth and the other 

 extinct animals characteristic of the Glacial period, the 

 trough of the Somme, about a mile in width and a hun- 

 dred feet in depth, has been eroded by the drainage of its 

 present valley. An extensive accumulation of peat also 

 has taken place along the bottom of the trough of the 

 river since it was originally eroded to its present level. 



* Lyell's Antiquity of Man, p. 321. 



