JTJEASSIC OF THE PAEIS EASIN. 



559 



This classification is the result of several modifications of pre- 

 vious ones, especially in the matter of names. 



The Upper Jurassic strata in the Boulogne area lie in an anti- 

 clinal whose crest has a slope from E.N.E. to W.S.W. Hence the 



Pig. 16.— Map of Part of the Boidonnais. (Scale 1 : 240,000.) 



lowest strata are seen in the E.N.E. corner, and the succession may 

 be traced by passing thence to the sea at Boulogne, whence a diver- 

 gence to the right or left will show the uppermost portions. The 

 development is also greater towards the S.W., as in the contrary 

 direction we approach the shore- line. Erom M. Pellat's beds E., 

 or the base of the Nerinsean limestones, downwards, the prevail- 

 ing character is argillaceous, and the comparatively feeble lime- 

 stones are merely intercalated masses, themselves usually more or 

 less marly. This feature renders the correlation somewhat difficult, 

 and has given rise to the complicated classifications of MM. Pellat 

 and Bigaux. 



The lower groups of clays, estimated by M. Pellat at 26 metres 

 in the north, but at 47 metres in the south-west, have not been spe- 

 cially examined. The uppermost portion, with Amm. cordatus and 

 Millericrinus, doubtless corresponds to the iSothe grits and clays, and 



