12 WHITE CHALK. 



exhibits so well the position and relation of the Gray Chalk, which contains so many 

 fine Echinidae, that I have introduced it here for reference. The strata lie in the following 

 descending order, and are collectively about 820 feet thick. 



1st. The Chalk with numerous flints ; it is about 350 feet thick, and maybe thus 

 divided : 



I. With few organic remains. 



II. A bed consisting chiefly of organic remains in which numerous flints of 



peculiar forms are interspersed ; and a few beds of flints run along it. 



2nd. The Chalk with few flints. This stratum is about 130 feet thick. 

 3rd. The Chalk loithout flints is 140 feet thick, and consists of — 



I. A stratum containing very numerous and thin beds of organic remains, 



90 feet thick. 



II. A stratum about 50 feet thick, with few organic remains. 



4th. The Gray Chalk. This is estimated to be not less than 200 feet in thickness, 

 and is that from which has been collected most of the fine specimens of Cidaris 

 Boiccrbankii, Eorb. ; Pseudodiadema omatum, Forb. ; P. tumidum, Forb. ; P. 

 variolar e, Brong.; P. Brongniarti, Ag. ; P. Mackiei, Wowd., Salenia Austeni, 

 Eorb. ; S. Clarkii, Eorb. ; S. gibba, Eorb. ; S. granulosa, Forb. ; and S. peta- 

 lifera, Defr., with other specimens of Chalk-marl species. 



The Lower Chalk and Chalk-marl are represented on the Continent by the Untcre 

 Kreide and Planer of the Germans, the Craie tuffeau of the French ; and the Etage 

 Turonien of d'Orbigny. 



THE WHITE CHALK. 



The uppermost portion of the Cretaceous formation extends across the island in an east 

 and west direction, from the Needles to Culver Cliff, and all its beds are fully exposed in 

 several magnificent coast-sections ; as these beds are nearly vertical or highly inclined 

 at Alum and Scratchells Bays on the east, and at Culver Cliffs on the west, the sub- 

 divisions of the whole Cretaceous formation, and the way the beds pass into each other, 

 may be most satisfactorily ascertained. The bands of flints are well displayed in Scratchells 

 Bay and Culver Cliffs, and there is a fine exposure of vertical Chalk strata in a pit on 

 Brading Down ; in all these localities, and many others which it is unnecessary to 

 enumerate, the flints appear as parallel layers at certain intervals in the strata, presenting 

 a striking contrast from their blackness to the snowy aspect of the Chalk with which they 

 are interstratified. 



" In consequence of the high angle at which the Chalk dips throughout the greater 



