92 GEOLOGY OF THE ISLE OF WIGHT. 



No section, however, occurs of t'lie higher beds forming the 

 Down, with the exception of a small hole on the east side of 

 Shankhn Down, which seems to be in the massive beds of the 

 Middle Chalk. On the very steep slope of chalk over Ventnor 

 a small spring rises, known as St. Boniface's Well. It was 

 remarked by Sir H. Englefield {op. cit. p. 37) that "a spring at 

 this height, is a most remarkable circumstance, and the only 

 instance of the kind in the whole island. It indicates some 

 stratum within the hill differing from the chalk, which certainly 

 would let the water sink through its substance here, as it does 

 everywhere else." This spring occurs at about the height at 

 which it may be calculated that the Melbouru Hock and 

 Belemnitella Marl should occur. 



Division of the Upper Chalk into Zones. 



The inland section of the Chalk-with-flints presents a remarkable 

 uniformity in lithological character. The sub-division of this 

 great mass by M. Barrois depended therefore principally on the 

 evidence of the fossils, which he collected himself. The following 

 account of the four zones is an abstract of the description published 

 by him in 1875.* The thickness of the various zones are given by 

 M. Barroir, in round numbers of metres. The conversion of metres 

 into feet gives a misleading impression of minuteness of measure- 

 ment. The zones are taken in ascending order. 



Zone of Holaster planus. 



For the base of this zone the seam of black clay, described on 

 pp. 87, 88, was chosen by M. Barrois. The zone is seen in the 

 Military Road cutting near Freshwater, as a very hard nodular 

 chalk about 65 feet thick. The nodules are of a yellowish-white 

 and very hard, so that it is difficult to detach some urchins, 

 which occur in them. The rock enclosing the nodules is softer, 

 and of a greenish-grey colour ; and numerous layers of homo- 

 geneous white chalk with nodules are intercalated. Tabular 

 layers of flint are abundant, and the zone is rich in fossils. At 

 Watcombe Bay, near Freshwater, where the rocks are continually 

 being scoured by the waves, there may be seen in every square 

 yard of the clifl all the fossils characteristic of the lower part of 

 the white Chalk. 



Zone of Micraster cor-tcstudinarium. 



This zone is exposed in parts of the cliffs scarcely accessible, 

 and is rarely quarried inland. It forms the centra! part of 

 the range ot Chalk Downs. The thickness is 160 to 170 feet, 

 but is difficult to estimate. The zone is exposed in pits at the 

 west of Benibridge Down, south-east of Brading Down, in the road 

 to the south of the great quarry on Arreton Down, in the road 



* Craie de I'lle de Wight, pp. 22-29. 



