Vol. 65.] GEOLOGY OF THE NEIGHBOURHOOD OF SEAFORD. 443 



Its physical features are illustrated by the accompanying diagram 

 (fig. 8, p. 456) photographed from a model, on the scale of 6 inches 

 to a mile, made for the purpose of this paper. Attention will be 

 drawn at a later stage to certain of these features, which will 

 be more intelligible when the stratigraphy of the country has been 

 explained. 



II. Stratigraphy. 



It is almost needless to say that this area does not differ from 

 the rest of the Sussex Downs in the scarcity of good inland 

 exposures. The few chalk-pits that exist are mostly overgrown, 

 and large stretches of bare turf, with few exposures of any kind, 

 except such as have been caused by small slips and rabbit-burrows, 

 increase the difficulty of mapping outcrops. For this reason I 

 confined my efforts to tracing the boundaries of the zone of Marsu- 

 pites lestudinarius, the limits of which are so clearly defined in the 

 cliff that some measure of success seemed to be possible inland. 

 Moreover, the delineation of the boundaries of this zone enables 

 the overlying zone of Actinocamaoc quadratus to be completely 

 mapped throughout this district, and of course indicates also the 

 upper limit of the underlying zone of Micraster cor-angninum. By 

 this means sufficient evidence is afforded of the general stratigraphy 

 of the district. 



Attention is first directed to the region east of the Cuckmere. 

 We know from Dr. Howe's work that the Marswpites-Z<me in 

 the cliff-section occupies the summits of four of the Seven Sisters 

 lying nearest to the river : so far as I can ascertain, the accuracy of 

 this conclusion admits of no doubt. Inland I have traced this zone 

 as far eastwards as the Birling Gap Valley, and it terminates on 

 the north in the long valley running from Jevington below Friston 

 towards West Dean. The zone occupies, in fact, the summit of an 

 eroded plateau which stretches between Friston and Cliff End at 

 the mouth of the Cuckmere. The main evidence for this con- 

 clusion I will recapitulate briefly. All round the Crowlink Valley 

 the Uintacrinus-Hajoidi can be distinguished. It occupies the highest 

 contours on the east of that valley, and is soon lost on descending 

 the hill towards East Dean. A good exposure of this band is seen 

 in an old pit on the hill-top due east of Crowlink Farm, where the 

 typical fossils can be collected. The bed seems to be clipping very 

 slightly towards the west, since it occurs at a somewhat lower level 

 on the western side of Crowlink Valley about a mile away. That 

 this bed terminates near Friston is indicated by a good exposure 

 below the windmill, facing west, where the top of the zone of 

 Micraster cor-anguinum is indicated by characteristic fossils, 

 among which the large form of Conulus albogalerus occurs in 

 some abundance. I shall have occasion to refer again to the 

 occurrence of this fossil in a band at the top of the zone of Micraster 



