154 POST-PLIOCENE ALLUVIUM OP ENGLAND. chap. ix. 



The alluvium of the Seine and its tributaries, like that of 

 the Somme, contains no fragments of rocks brought from any 

 other hydrogTaphical basin ; yet the shape of the land, or 

 fall of the river, or the climate, or all these conditions, must 

 have been very different when the graj* alluvium in which 

 the flint tools occur at Paris was formed. The great size of 

 some of the blocks of granite, and the distance which they 

 have travelled, imply a power in the river which it no longer 

 possesses. AVe can scarcely doubt that river-ice once played 

 a much more active part than now in the transjiortation of 

 such blocks, one of which may be seen in the Museum of the 

 Ecole des Mines at Paris, three or four feet in diameter. 



Post-pliocene Alluvium of England, containing Works of Art. 



In the ancient alluvium of the basin of the Thames, at 

 moderate heights above the main river, and its tributaries, 

 we find fossil bones of the same species of extinct and living- 

 mammalia, accomjianied by recent species of land and fresh- 

 water shells, as we have shown to be characteristic of the 

 basins of the Somme and the Seine. We can scarcely there- 

 fore doubt that these quadrupeds, during some part of the 

 post-pliocene period, ranged freely from the continent of 

 Europe to England, at a time when there was an un- 

 interrupted communication by land between the two 

 (countries. The reader will not therefore be surprised to 

 learn that flint implements of .the same antique type as 

 those of the valley of the Somme have been detected in 

 British alluvium. 



The most marked feature of this alluvium in the Thames 

 valley is that great bed of ochrcous gravel, composed chiefly 

 of broken and slightly ^vorn chalk flints, on which a great 

 ])art of London is built. It extends from above Maidenhead 

 through the metropolis to the sea, a distance from west to east 



