106 GEOLOGICAL DESCRIPTION OF THE SOMME YALLEY. CHAP. vn. 



CHAPTER VII. 



PEAT AND POST-PLIOCENE ALLUVIUM OF THE YALLEY OF THE 



SOMME. 



GEOLOGICAL STRUCTURE OF THE VALLEY OF THE SOMME AND OF 



THE SURROUNDING COUNTRY POSITION OF ALLUVIUM OF DIFFERENT 



AGES PEAT NEAR ABBEVILLE ITS ANIMAL AND VEGETABLE CON 

 TENTS WORKS OF ART IN PEAT PROBABLE ANTIQUITY OF THE 



PEAT, AND CHANGES OF LEVEL SINCE ITS GROWTH BEGAN FLINT 



IMPLEMENTS OF ANTIQUE TYPE IN OLDER ALLUVIUM THEIR VARIOUS 



FORMS AND GREAT NUMBERS. 



Geological Structure of the Somme Valley. 



rFHE Valley of the Somme in Picardy, alluded to in the last 

 J- chapter, is situated geologically in a region of white 

 chalk with flints, the strata of which are nearly horizontal. 

 The chalk hills which hound the valley are almost everywhere 

 between 200 and 300 feet in height. On ascending to that ele 

 vation, we find ourselves on an extensive table-land, in which 

 there are slight elevations and depressions. The white chalk 

 itself is scarcely ever exposed at the surface on this plateau, 

 although seen on the slopes of the hills, as at b and c (fig, 7 ). 

 The general surface of the upland region is covered continu 

 ously for miles in every direction by loam or brick-earth (No. 4), 

 about five feet thick, devoid of fossils. To the wide extent of 

 this loam the soil of Picardy chiefly owes its great fertility. 

 Here and there we also observe, on the chalk, outlying 

 patches of tertiary sand and clay (No. 5, fig. 7), with eocene 

 fossils, the remnants of a formation once more extensive, and 

 which probably once spread in one continuous mass over the 

 chalk, before the present system of valleys had begun to be 

 shaped out. It is necessary to allude to these relics of 



