(Chalk Avith flints). 



76 GEOLOGY OF THE ISLE OF WIGHT. 



In 1875 M. Barrels published his DescrijJtion Gkologique de la 

 Craie de V Tie de Wiglit/ui 'w\i\Qh he gives an exhaustive account 

 of the literature, physical features, zones, and fossil contents of 

 the Chalk. The sub-divisions which he adopted are as follows in 

 descending order : — 



rZone a Bclermiitelles 80 metres 

 I (= 262^ feet). 



I Zone a Micraster curanguinum, Ag. 

 Craie Blanche J 160 metres {= 524^ feet), 



o 11 — -L,. n-..^^\ ^ Zone a Micraster cor-testudinarlum, 



Gold, 50 metres (= 164 feet). 

 Zone a Holaster jilanus, Ag. 20 metres 

 {=^ Qo\ feet). 

 rZone a Terchratulina gracilis, D'Orb. 

 Craie Marneiise J 20 metres (= 65| feet). 



(Chalk without flints). | Zone a Inoceramus labiahis Schloth. 



L 40 metres (==131 feet). 



^ ^1 11 /-.I n AT 1 fZoue a Scaphites CBqualis, Sow. 

 Grey Chalk, Chalk Marl | 3. ^^^.^^^^ ^^ ^^^ ^^^/^^ 



He stated that his zone of Inoceramus labiatus has as 

 its base a bed of very hard yellowish nodules imbedded in a 

 o-reenish grey marl ; this he correlated in 1876 with the Melbouru 

 Eock,* He gave additional particulars concerning the Chalk Rock 

 of Mr. Whitaker, which occurs near the top of his zone of 

 Terebratvlina gracilis, and noticed a third nodular horizon in the 

 lower part of the zone of Holaster planus. 



Thus it will be seen that there is a general agreement as to the 

 main divisions of the Chalk. The names Upper, Middle, and 

 Lower Chalk are here used in place of tho^^e formerly employed, 

 so as to bring the nomenclature into accordance with that of the 

 mainland. 



The Lower Chalk, which passes insensibly down into the 

 Chloritic Marl, consists of alternations of chalk with shaly and 

 pale-blue marl, in beds of six inches to two feet in thickness. 

 Towards the lower part it is impure, and contains glauconite, or 

 even rolled phosphatic nodules, but upwards the proportion of 

 chalk increases at the expense of the marly bands, the more 

 massive rock thus produced constituting the "grey chalk" of 

 some authors. This sub-division forms generally ihe first rising 

 ground at the foot of the Downs. It has been extensively dug 

 for agricultural purposes, and the old pits have yielded a great 

 number of fossils, ^mor\g\\\nc\\ Ammonites rhotomagensis,A. varians, 

 and Scaphites aqualis are the most persistent. 



The Middle Chalk, of which the Melbourn Rock constitutes the 

 base, coneists of massive beds of chalk from 3 to 6 feet in thick- 

 ness, with partings of marl 2 or 3 inches thick. It forms the 

 steeper part of the slope of the Downs, and is exposed in the 

 upper part of many of the pits in which the Chalk Marl has been 



* Ann. Soc. Geol. Nord, t. iii., juin 1876. 



