Wealden District and the Bas Boulonnais. 29 



The top of Mont Lambert is the highest point within a considerable distance 

 of Boulogne. The extensive quarries near its summit are easily recognised as be- 

 longing to the upper sand. In descending in any direction we soon arrive at the 

 upper division of the Kimmeridge clay, and along the road to Boulogne the siliceous 

 beds beneath it are distinctly seen. These descend the hill on the north side 

 across the St. Omer road down to the upper part of the valley of the Denacq, 

 already noticed as ranging with the La Creche line of elevation, where I found 

 them near the upper extremity of the valley abutting directly against the upper 

 division of the Kimmeridge clay (Diagram No. 30.). This distinctly proves the 

 continuation of the La Creche line up to this point. It probably dies away some- 

 what east of it. 



At the point just mentioned the clay was identified by the oyster shells ; and, 

 moreover, I traced it along the brow of the hill on the east of the valley of the 

 Denacq, which shows that a great fault also ranges along the lower part of that 

 valley down to Wimille, since it has been shown that the upper division of the 

 Kimmeridge clay passes down to the bottom of the valley on its western side. 



When the clay on the east side of the valley of the Denacq meets the valley of 

 the Wimereux, it ranges along its south side at the same elevation. It also con- 

 stitutes the hill on the north side of the valley nearly to the summit immediately 

 east of the Calais road ; consequently we have no longer the same evidence of a 

 great fault ranging along this valley east of Wimille, as on the west of that place. 

 There are evidences of disturbance, however, on the north side of the valley. South 

 of Maninghen I found the beds in a newly-opened pit dipping very rapidly to the 

 north. About Souvremouhn there were indications of cross fractures, by which 

 the lower beds of the Kimmeridge clay are brought nearer the bottom of the valley 

 than either to the east or west of that place. I have no doubt therefore that the dis- 

 location, in which the valley west of Wimille undoubtedly originated, was continued 

 to the east of that place. It probably dies away towards the upper part of the 

 valley in the same manner as in the La Creche line. 



From the high ground north of the Wimereux, and between the coast and the 

 Calais road, the upper division of the Kimmeridge clay may be traced, gradually 

 descending towards the Ambleteuse valley as in the coast section, the declination 

 of the strata in that direction however being less, as far as 1 could judge, at points 

 more remote from the coast. At Auxdresselles, the northern extremity of the 

 Ambleteuse dunes, we find some hard siHceous beds rising from beneath the valley, 

 and apparently also from beneath the upper division of the Kimmeridge clay. The 

 portion at the level of the beach being disintegrated by the waves, leaves the shore 

 strewed with enormous blocks, exactly similar to those which are found also on the 

 beach at La Creche, and they belong, I conceive, to the same bed. North of Aux- 



