Vol. 65.] GEOLOGY OF THE NEIGHBOURHOOD OF SEAFOED. 451 



With regard to Bourgueticrinus, I found nipple-shaped heads in 

 the Marsujrites-Zone, and dumb-bell shaped ossicles in the zone of 

 Actinocamax quadratus ; but with me these were apparently rare 

 occurrences. Barrel-shaped ossicles at the top of the zone of 

 Micraster cor-anguinum seemed to be by far more common. 



I attach no importance to my negative results, because my 

 object was rather to map the outcrops than to make long lists of 

 fossils. The exposures, too, are far too poor to enable such lists 

 to be easily secured. 



III. Structural Features. 



It is now possible to consider the structural features of the Chalk 

 in this area. In the country north and west of Seaford, between 

 the Cuckmere and the Ouse, it has been shown that the beds dip 

 gently towards the south-west, at an angle of 2°, with no sign of 

 any appreciable flexure. At Hindover, the top of the Marsupites- 

 Zone is at an altitude of about 225 feet above O.D., whence it sinks 

 gradually towards the south until, near Chyngton, it lies below the 

 level of the alluvium of the Cuckmere, to rise again along the slope 

 of Seaford Head to a height of 287 feet O.D. Thus, while there is 

 a gentle southerly dip-slope from Hindover to Chyngton, there is a 

 steep northerly dip-slope from the latter place to the top of Seaford 

 Head. The strike of the beds at Seaford Head has been shown to 

 be nearly east and west. Evidently, therefore, Seaford Head has 

 been carved out of the limb of a sharp flexure, with its steep face 

 towards the north. This fold, only a fragment of which remains, 

 apparently resembles in form the uniclinal fold of the Isle of Wight, 

 and, as in that case, appears to have been caused by a thrust from 

 the south. It is this flexure which brings up the zone of Micraster 

 cor-testudinarium along the base of the cliff between Cuckmere 

 Haven and Seaford Head, in the fine coast-section described by 

 Dr. Rowe. 



On the opposite side of the narrow Cuckmere Valley, however, 

 not a trace of this flexure exists. As has been shown above, the 

 beds are there nearly horizontal, with a very slight general 

 inclination towards the south-west. This same feature can be seen 

 also in the flint-bands in the Micraster cor-anguinum-Zone along 

 the eastern side of the Cuckmere Valley. The uniclinal fold of 

 Seaford Head, therefore, comes to a sudden termination somewhere 

 in the Cuckmere Valley. A difference in level of nearly 300 feet 

 occurs between the nearly fiat Marsupites-Zone on the plateau east 

 of the Cuckmere, and the same bed at the bottom of the trough 

 beneath Chyngton. Only two interpretations of this fact seem 

 possible : either the fold dies out, or there is a fault in the 

 Cuckmere Valley. 



I discard the first supposition because the distance is too short, 

 and whatever westerly pitch the fold may have it is too small to 



