106 GEOLOGICAL DESCRIPTION OF THE SOMME VALLEY, chap. vii. 



CHAPTER Vn. 



PEAT AND POST-PLIOCENE ALLUVIUM OF THE VALLEY 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 CONTENTS 



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 ASomme Valley. 



milE Valley of the Somme in Piciirdy, alluded to in the last 

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

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

 The chalk hills which bound the valley are almost every where 

 between 200 and oOO feet in height. On ascendingto 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 I'egion 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 S])read in one continuous mass over the 

 chalk, before the present system of valley's had begun to be 

 shaped out. It is necessary to allude to these I'elics of 



