50 Mr. Hopkins on the Structure of the 



clay in the valley at Bainctun. At the eastern end of the section, the cretaceous 

 system is again observed to rest immediately on that clay, as does the lower part 

 of it also in the Foret de Desvres. These sections are on a scale about twice as 

 great in length as those of the Wealden district; section (29) is on a scale about 

 eight times as great. It is a section of the coast north from Boulogne. The line 

 of La Creche is finely exhibited in the cliff. The section also shows the fault at 

 Wimereux ; the beds continued from La Creche to a beneath the surface of the 

 sea, would on the north side of the fault be found at a', if they still existed there, as 

 they do within less than a mile of the beach. From the fault the beds are observed 

 to descend towards the north into the next valley ; from which they rise again on 

 the north of Auxdresselles, forming the third line represented on the map, in pro- 

 ceeding northward from Boulogne. Section 30 shows the fault by which the 

 valley of the Denacq is formed, and section 31 represents that of Montlambert in a 

 direction perpendicular to that given in (28) ; it also shows the continuation of the 

 line of La Creche near the St. Omer road, where it assumes the character of a 

 fault. The valley of the Denacq on meeting this fault assumes its direction. 



In these sections, the beds between the gault and Kimmeridge clay are not 

 distinguished from each other. The upper portion of these beds is undoubtedly 

 the lower greensand of our own country. The lower portion is considered to belong 

 to the Portland formation. The former portion consists almost entirely of ferru- 

 ginous sand ; the latter contains huge calcareous blocks, sometimes forming irre- 

 gular beds, which are worked, in many places, for building and other purposes. 

 There are large quarries of this kind on Montlambert, where the beds are imme- 

 diately above the Kimmeridge clay ; and also near the column of Napoleon^ imme- 

 diately on the north side of the fault of La Creche, by which, on the south side, the 

 lower beds of the Kimmeridge clay are brought up to the level of the quarries. 



