446 MR. J. V. ELSDEN ON THE [Aug. I909, 



Zone. Traverses were first made for the purpose of determining 

 the northern extension of the zone of Actinocamaoc quadratus, which 

 is readily traced from the west of Seaford Head northwards to the 

 top of Hindover, immediately beneath which, on the south side, the 

 Bryozoa-Bed is strongly marked. By a systematic examination of 

 the beds in the Cuckmere valley, from Alfriston towards the south, 

 it was soon found that the key to the position of the Marswpites- 

 Zone lay in the steep slope of Hindover, where, despite the absence 

 of really good exposures, numerous small slips in the Chalk afford 

 fair opportunities for collecting at successive horizons. This section 

 gave me much trouble, but the sequence finally proved to be as 

 follows : — The upper part of the northern face of the slope, about 

 75 feet in depth, as measured by the aneroid, is in the zone 

 of Actinocamaoc quadratus. The evidence is quite complete ; 

 Cardiaster pillula and the gibbous form of Echinocorys scutatus 

 occur, and near the base the passage-beds with bryozoa and the 

 Ostrea-ivegmanniana Band are recognizable. A few feet below this 

 plates of Marsupites are to be found in quantity. Lower still may 

 be recognized the Uintacrinus-H&ndL ; and the top of the zone of 

 Micraster cor-anguinum is again distinguished by a well-defined 

 band of Conulus albogalerus and other characteristic species. A 

 similar sequence can be identified on several traverses of this hill. 

 The top of the Marsupites-Zone is here at a height of about 225 feet 

 above the river. 



The outcrop of this zone can now be followed westwards along 

 the steep face of the deep dry valley in which are situated Pinchem 

 and Hobb's Hawth. This valley for some distance follows the 

 general strike of the Chalk, but winds northwards as it approaches 

 the watershed. In consequence, the outcrops rise in level along 

 the valley, and the Uintacrinus-~BsLn& crosses the watershed at an 

 altitude of 300 feet. This fact was readily proved by finding 

 Uintacrinvs and Terebratulina Rowei in some rabbit-burrows just 

 below the ridge at that altitude. The bottom of this valley 

 throughout is in the zone of Micraster cor-anguinum, typical 

 fossils occurring in numerous small exposures near the base. The 

 whole of the ground sloping southwards, between this valley and 

 the sea, is in the zone of Actinocamax quadratus, all the available 

 openings yielding unmistakable evidence of this horizon. 



Passing over the watershed westwards along Beacon Hill, direct 

 evidence is scanty, owing to the scarcity of good exposures. The 

 configuration of the ground, however, shows that the outcrop of 

 the Marsupites-Zone should follow the steep face of Beacon Hill 

 towards the west, until the bold north-and-south ridge, extending 

 from Denton to Bishopstone, is reached. This ridge is best attacked, 

 in the first instance, on the western flank. At Denton village a 

 chalk-pit in the lower part of the hill again shows the Conulus- 

 albogalerus Band, which, as at Friston and Hindover, marks the 

 top portion of the zone of Micraster cor-anguinum. This zone is 



