390 



E. M. BURWASH CHALK AXD FLIXTS OF XORTHEKX FEAXCE 



(at Abbeville j, the Bresle (at Le TrepDit). ^nd the Bethune (at 

 Dieppe). The Seine forms the southem boundarT of the area under 

 consideration from Le Havre to Eoiien, after which its margin may be 

 taken as extending eastvrardly to the neighborhood of Soissons. The 

 sketch-map which accompanies this article will sei*ve to indicate the pro- 

 portion of this area which is underlain by the chalk and to give some 

 idea of its drainas'e svstem. 



Figure 1. — Map of northern France 

 Showing dissection of the "chalk formations. 



The Eivees of the Eegiox axd their Actiox 



The main rivers occupy mature valleys floored with alluvium during 

 the greater part of their courses, and the interstream uplands, in most 

 cases, have level tops, where they are at all extensive, with easily flowing 

 weather curves on their sides, due to the softness and solubility of the 

 underlying chalk. These flowing curves are, however, often interrupted 



