26 Mr. Hopkins on the Structure of the 



it the liiglily inclined beds of still lower formations, on which the chalk itself seems 

 immediately to repose. In the north-east corner of the district, the cretaceous 

 system overlies the upturned edges of the mountain limestone with its beds of coal ; 

 till we come to the south of the river which bounds the older formations, where 

 the lower greensand is found to repose on the Oxford clay along the whole boundary 

 of the district by Boursin, Colemberg, Henneveux, Brunembert, Lottinghen, and 

 Desvres. To the south-west of the latter place, and at Samer, the greensand lies 

 immediately on the coral rag ; and along the southern boundary it reposes also on 

 that formation or on the Kimmeridge clay. 



Oxford Clay. — The hill north-west of Marquise, on which the village of Basinghen 

 is situated, presents to the east an escarpment of considerable elevation, the upper 

 part of which is occupied by the Oxford clay, and the lower part by the oolitic beds 

 immediately beneath it (Diagram No. 26.). These latter beds extend a little to the 

 west of the Marquise and Calais road, where they form a thin and unconformable 

 covering to the lower part of the platform formed by the surface of the mountain 

 limestone. 



At some distance north of the village, the Basinghen Hill takes a north- 

 westerly direction ; and from that point the Oxford clay descends and passes under 

 the upper formations nearer the coast. On the south of Basinghen it likewise 

 descends towards the south and passes beneath the valley of the Ambleteuse river. 

 The coral rag also bassets out on the high ground west of Basinghen, passing 

 down to the above-mentioned valley, and under the Kimmeridge clay which occu- 

 pies the coast from Ambleteuse to the dunes at Wissant. 



On the south of the Ambleteuse river the Oxford clay forms an escarpment 

 similar to that at Basinghen, but is at a greater distance from the coast (Diagram 

 No. 26.) . It passes from the east of Wievre EfFroy to meet the valley of the Wimereux 

 near Belle. On the south of that valley the high ground is projected eastward beyond 

 Alinctun, where the Oxford clay still rises to the brow of the hill by Henneveux 

 and Brunembert, as far as the Liane. The same formation also occupies the whole 

 of the district east of this line of hill, till it is concealed beneath the unconformable 

 covering of the cretaceous system as previously described. On the south of Bru- 

 nembert the escarpment takes the westerly direction of the Liane, the upper part 

 being formed of the coral rag and the lower of Oxford clay, the lower part of 

 which probably stretches over the surface of the greater part of the valley com- 

 prised between the above escarpment on the north, the forest of Desvres on the 

 west, and the boundary hills on the east and south. Thence it passes under the 

 eminence on which the forest just mentioned is situated, and rises in the hill which 

 still follows the course of the Liane in the south-westerly direction which that 

 river suddenly assumes, till it meets the road from Boulogne to Desvres, near 



