BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 30, pp. 389-398 September 30, 1919 



CHALK, FLI^TTS, AND GEOUND-WATEE OF NOETHEEN 



FEANCE ^ 2 



{Presented before the Society December 21 , 1918) 



BY EDWARD M. BURWASH 



CONTENTS 



Page 



Tlie area studied 389 



The rivers of the region and their action 390 



Theory of formation of flint nodules 392 



Source of the silica 393 



Ground-water 394 



Underground streams 395 



Development of the valleys 396 



Relation of the streams to the water-table 398 



The Area studied 



During the last four years of war the British military base in France 

 has included practically all the seaports from Calais to Le Havre, and 

 the roughly triangular area between this coast and the part of the front 

 held by them was traversed by their lines of communication and occu- 

 pied by base depots, training camps, hospitals, rest camps, railway con- 

 struction troops, and other auxiliary forces to an extent which involved 

 a very large temporary increase in its normal population. It is nearly 

 all underlain by the chalk formation, with the exception of Jurassic areas' 

 around Boulogne and to the southwest of Amiens, a Tertiary area which 

 covers the Belgian part of the front and extends nearly as far west as 

 Calais, and another between the Somme and Canche rivers to the north of 

 Amiens. To the south of the line of highlands which runs southeast- 

 wardly from Cape Gris N"ez the rivers follow a northwesterly course to 

 the sea, and are, in order from north to south, the Liane, which reaches 

 the sea at Boulogne; the Canche (at Etaples), the Authie, the Somme 



1 Entered in the program of the meeting as "Subterranean chalk-streams of northern 

 France." 



2 Revised manuscript received by the Secretary of the Society January 15, 1919. 



(389) 



