154 POST-PLIOCENE ALLUYIUM OF 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 hydrographical 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 grey 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. We can scarcely doubt that river-ice once played 

 a much more active part than now in the transportation 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, accompanied 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 therefore 

 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 uninterrupted 

 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 ochreous gravel, composed chiefly 

 of broken and slightly worn chalk flints, on which a great 

 part of London is built. It extends from above Maidenhead 

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



