460 GEOLOGT OP THE NEIGHBOURHOOD OF SEAEORD. [Aug. I9O9, 



the escarpment of the South Downs was once united with that of 

 the Boulonnais, and not with that of the Isle of "Wight. 



The relief-model exhibited showed well how the remarkably 

 horizontal appearance of the Micraster cor -testudinarium- Zone 

 between Seaford Head and the Cuckmere was accounted for by the 

 coast-line being coincident with the strike of the beds. It was 

 probable, however, that the dip of the lower beds was not so great 

 as that of the upper beds as in the Isle of Wight, for otherwise 

 the inward dip would have been betrayed in the indentations of 

 the cliffs. 



He was not quite in accord with the Author as to the origin 

 of the dry Chalk valleys, but time would not allow of discussion of 

 that part of the paper. 



Mr. 0. T. Jones wished to ask the Author whether he had con- 

 sidered an alternative explanation of the relations of the fold and 

 the fault which he described. The speaker suggested that the 

 fault might be later than the uniclinal fold, and that the flat-lying 

 beds on the east of the fault might correspond to a part of the 

 fold-structure lying north or south of the trough, and where 

 therefore the beds would be nearly horizontal. The state of 

 affairs described by the Author might have been brought about 

 by a horizontal movement along the fault, which shifted the axis 

 of the fold northwards or southwards and brought the flat-lying 

 beds against the centre of the trough. 



The Rev. E. C. Spicer pointed out that the Chalk area of the 

 district had strongly marked surface-features, while the adjacent 

 Tertiary area had low relief. It was difficult to realize how any 

 denuding agency could produce such markedly different results in 

 the same area by mechanical erosion at the surface. If the Chalk 

 area is being modified by solution-activity, these morphological 

 differences could be more easily understood. 



Dr. J. W. Evans thought, with reference to a previous speaker's 

 suggestion, that it was more natural to suppose that the folding 

 on the west side of the fault was part of the same movement as 

 that which caused the fault, than that the fold was first formed 

 and subsequently dislocated. Dip-faults were, in fact, usually the 

 outcome of the difference in flexuring on the two sides of a 

 fracture (' Economic Geology ' vol. ii, 1907, p. 805). 



The Author said that, although the Marsupites-OhdXk possessed 

 distinct lithological characteristics, these were not sufficiently 

 definite to enable boundary-lines to be drawn with certainty by 

 that means alone. As to the precision with which these lines 

 could be fixed in the field, in this area the zonal limits were very 

 sharply defined. Below the lowest Cardiaster-pillula Band, which 

 was taken as the base of the Actinocamax-quadratus Zone, were 

 20 feet of easily recognizable passage-beds before the top of the 

 Ilarsujrites-B&nd (about 50 feet thick) was reached. Then came 

 the Uintacrinus-Band (about 30 feet thick), below which a Comdus- 



