28 Mr. Hopkins on the Structure of the 



Structure of the District near the Coast. — Commencing with the coast section 

 from Boulogne (Diagram No. 28.) and proceeding northward, we observe that the 

 stony bands which separate the two portions of the Kimmeridge clay are brought 

 down from the top of the cliff to the beach, by a rapid curvature of the beds, at 

 La Creche. These beds then dip beneath the level of the sea, and the cliff, from 

 that place to the mouth of the Wimereux, is composed, in its lower part, of the 

 upper division of the Kimmeridge clay, the higher portion of the cliff consisting of 

 the superincumbent sandstone beds above described. In this part of the cliff there 

 is a considerable dip to the north which carries the upper surface of the Kimme- 

 ridge clay below the level of the sea at the dunes at the mouth of the Wimereux. 

 On the north of the dunes, however, the upper division of that formation is found 

 at a considerable altitude. It afterwards descends again with a gentle dip to the 

 north beneath the Ambleteuse dunes. It ranges also to the eastward along the 

 north side of the valley of the Wimereux, where it may be distinctly traced nearly 

 as far as the Calais road, ascending by the gentle eastward rise of the beds nearly 

 to the top of the hill. I identified it at the mouth of the Wimereux and also near the 

 Calais road by the deltoid oyster ; and moreover, near to the village of Wimille, 

 the lower bed of Kimmeridge clay is distinctly recognised in the lower part of the 

 valley by the abundance of the Gryphcea virgula. Returning to the top of the cliff 

 at La Creche, we find distinct evidence of the continuance, in a direction parallel 

 to the Wimereux, of the line of flexure of which the section is so beautifully exhi- 

 bited in the cUff. The junction of the upper sand on the north with the lower 

 Kimmeridge clay on the south, which marks the course of the line, may be distinctly 

 traced close by the fort near La Creche, to the north of the column of Napo- 

 leon, into the upper part of the valley of the little river Denacq. In some part of 

 this range it probably becomes a line of fault. 



On the north of this line it is easy to trace the upper division of the Kimmeridge 

 clay with the superincumbent upper sand down to the valley of the Wimereux (to 

 which it descends in the same manner as in the cliff) and also to the Denacq. The 

 windmill about three-quarters of a mile from Wimereux, on the Boulogne road, 

 stands on the clay (Diagram No. 29.), which also appears at the Uttle hamlet north 

 of the column, whence it passes northward under the quarries in the upper sand near 

 that spot. In a quarry also near to Wimille, and between the great road and the 

 Denacq, the beds of that formation are found to dip rapidly into the valley. Hence 

 then the upper division of the Kimmeridge clay passes into the bottom of the 

 valley of the Wimereux on its southern side, while on the northern side, as already 

 shown, it occupies nearly the top of the hill. Consequently there must be a very 

 large fault ranging along that valley from the coast to the village of Wimille 

 (Diagram No. 29.). 



