508 STKATIGKAPHICAL GEOLOGY 



The complete succession of the zones exposed between Dover and 



Margate in descending order is as follows : 



Feet. 



Soft chalk in two sub-zones, the upper characterised by Marsupites 

 and Uintacrinus, the lower by Actinocamax yranulatus, and 

 A. verus also occur . ........ 116 



Zone of Micr. coranguinnm. Smooth chalk with many layers of 

 black flints ; Cidaris sceptrifcra, C. pcrornata, Galcrites 

 conicus, and Cyphosoma Kcenigi . . . . . .250 



Zone of Micr. cortestudinarium. Rough nodular chalk with 



many flints ; Micraster precursor and Hoi. placenta . . 75 



Zone of Holaster planus (as above described) . .... 45 



486 



On the coast of Sussex, however, higher zones come in. The 

 Marsupite zone has been identified at Seaford Head, and above it 

 is 170 feet of chalk containing Offaster pilula, Actinocamax 

 granulatus, Ccelosmilia laxa, and other fossils of the quadratus 

 zone. This chalk extends westward from Newhaven to Brighton, 

 and thence to the valley of the Arun, where a succession of quarries 

 between Houghton and Arundel shows parts of all the zones above 

 mentioned (see Fig. 173). Still farther west chalk containing 

 Belemnitella mucronata has been found, and this highest zone 

 underlies the Eocene of Hampshire and is well exposed in quarries 

 on Portsdown Hill, where an inlier of chalk is brought up 

 within the Tertiary area by an anticlinal flexure. The total 

 thickness of the Upper Chalk in West Sussex and Hampshire 

 must be from 800 to 900 feet. 



In the Isle of Wight the Upper Chalk forms a long and narrow 

 outcrop across the centre of the island in consequence of the steep 

 dip imparted to it by the flexure which carries them below the 

 Eocene of the Hampshire basin (see Fig. 172). Its thickness is 

 from 1200 to 1300 feet, and the thicknesses of the several zones at 

 the western end of the outcrop, as recently determined by Mr. 

 Rowe's measurements, are as follows : 23 



Feet. 

 Zone of Bel. mucronata. White chalk with flints, Echinocorys 



(pyramidal form), Gidaris serrata, Magas pumilus . . . 475 

 Zone of Act. quadratus. White chalk with some marl seams but 



few fossils 342 



Zone of Marsupites. Compact white chalk with flints ... 80 

 Zone of Micraster coranguinum. Chalk with many layers of flint 



nodules and the usual fossils ....... 310 



Zone of Micraster coriestudinarium. Rough nodular chalk with 



flints 53 



Zone of Holaster planus. Hard greyish nodular chalk . . 60 



1320 



