356 MAN AND THE GLACIAL PERIOD. 



This substance occurs all along the bottom of the valley 

 from far above Amiens to the sea, and is in some places 

 more than thirty feet in depth. The animal and vegeta- 

 ble remains in it all belong to species now inhabiting 

 Europe. 



The depth of the peat indicates that when it was 

 formed the land stood at a slightly higher elevation than 

 now, for the base of the stratum is now below the sea- 

 level, while the peat is of fresh-water origin, and, accord- 

 ing to Dr. Andrews,* is formed from the vegetable ac- 

 cumulations connected Avith forest growths. When, there- 

 fore, the. country was covered with forests, as it was in 

 prehistoric times, the accumulation must have proceeded 

 with considerable rapidity. This inference is confirmed 

 by the occurrence in the peat of prostrate trunks of oak, 

 four feet in diameter, so sound that they were manufact- 

 ured into furniture. The stumps of trees, especially of 

 the birch and alder, were also found in considerable num- 

 ber, standing erect where they grew, sometimes to a height 

 of three feet. Now, as Dr. Andrews well remarks, it is 

 evident that, in order to prevent these stumps and pros- 

 trate trunks from complete decay, the accumulation of 

 peat must have been rapid. From certain Roman remains 

 found six feet and more beneath the surface, he estimates 

 that the accumulation since the Roman occupation has 

 been as much as six inches a century, at which rate the 

 whole would take place in somewhat over 5,000 years. 



Still, if we accept this estimate, we have obtained but 

 a starting-point from which to estimate the age of the 

 high-level gravels in which palaeolithic implements were 

 found ; for, if we accept the ordinary theory, we must add 

 to this the time required for the river to lower its bed 

 from eighty to a hundred feet, and to carry out to the sea 

 the contents of its wide trough. But, as already shown, 



* American Journal of Science, October, 1868. 



