Revietvs — 31. Barrois — Chalk of the Isle of Wight. 129 



when touched. The Chalk here is capped by a gravel containing 

 numerous flints, in which M. Barrois found an implement. 



The northern mass, which traverses the island in an east and west 

 direction from Culver Cliff to the Needles, is divided by the author 

 into three portions. The first extends from the Needles to Calbourne 

 Bottom, the second from Calbourne Bottom to the Medina, and the 

 third from the Medina to Culver Cliff. In the two lateral portions 

 the hills are higher and the dip of the beds greater than in the central 

 one. In the former the dip is from 40° to 80°, whilst in the latter 

 it is only from 10° to 45°. 



This mass is also divided by four north and south faults. Through 

 the most important of these the Medina flows ; the next has formed 

 Calbourne Bottom, and gives rise to the spring at Calbourne ; whilst 

 two other fractures have allowed the Yar and Eastern Yar to cut 

 through the Chalk at those points. 



The author divides the Chalk composing this ridge of hills into 

 the following zones, taking them in ascending order : 



I. — Chalk Marl (zone of Scaphites cequcdis). Blue-grey, marly 

 limestone, with conchoidal fracture, containing nodules of iron pyrites. 

 Fossils abundant in lower portion. 



II. — Craie Marneuse — Chalk without flints : 



1. Zone of Inoceramus labiatws. — Hard, dry, yellowish- white Chalk, marking but 

 slightly, nodular at the base for about two yards, but becoming more homogeneous as 

 it passes up. Quarried at Mount Joy and Mefsty Down. 



2. Zone of Terehratulina gracilis. — About 16 feet thick. Towards the upper part 

 is a band of nodules of hard Chalk covered with a green coating, and containing 

 nearly 4| per cent, of phosphate of lime. This band, called " Chalk Rock" by Mr. 

 Whitaker, can be traced from one end of the island to the other. A stratum of 

 Chalk, less marly than that below the nodules, succeeds them, containing a large 

 number of T. gracilis, but no flints. This again is covered by a layer of black clay, 

 from less than one to four inches thick. This layer of clay the author considers to be 

 the true line of demarcation between the Chalk without and the Chalk with flints, 

 as it separates two distinct zones of life; whereas the " Chalk Eock," which Mr. 

 Whitaker took as the dividing line, does not do so. 



III.— Chalk with flints : 



1. Zone of Holaster jjkoius. — Hard nodular Chalk, full of fossils, about 66 feet 

 thick. The nodules are extremely hard, and of a yellowish-white colour, the Chalk 

 between them being softer and greenish-grey in colour. Bands of tabular flint are 

 numerous ; the flint nodules are small and scattered irregularly through the mass. 



2. Zone of Micraster cor-aiiguinum. — Chalk much fissured. Flints abundant in 

 rows and tabular masses. Sections scarce. About 1 65 feet thick. 



3. Zone of Micraster cor-testudinarum. — Compact, soft, dazzling-white Chalk, 

 containing black angular flints in rows, from 20 inches to 3 feet apart, which towards 

 the upper part are replaced by bands of grey marl. Fossils are not numerous. 

 Thickness about 550 feet. 



4. Zone of Bdemnitellce. — In the lower portion the Chalk is white, marks well, 

 and contains many large black flints. Echinocorys gibhus abundant, along with 

 Belemnitella mucronata and B. quadrafa. The upper portion is softer, and marks 

 more easily. The flints are smoky-grey coloured. B. mucronata with Magas 

 pumilus very abundant. The latter is not found in the lower portion. 



At Arreton Down Quarry this zone is found superimposed wpon 

 the last. The distinction between these two zones rests on palason- 

 tological evidence only. 



The Chalk with BelemniteUxB is directly covered by the Tertiaries, 

 and is in many places eroded and pierced with sand-pipes. A deep 



DECADE II. VOL. III. — NO. III. 9 



