73 



CHAPTER Vir. 



THE CHALK. 



Introduction. 



This formation extends completely across the Island in an east 

 and west direction from the Needles to Culver Cliff. It may be 

 examined both in the sea-cliffs and in the numerous pits Avith which 

 its surface is covered throughout the entire distance between those 

 points. It forms a range of elevated undulating hills, conspicuous 

 from afar on account of their altitude, and the bold rounded 

 outline they present to the eye, as well as from their bare and 

 uncultivated surface, which is covered with a short grass, and is 

 rarely used for any other purpose than the pasturage of sheep. 

 In consequence of the high angle at which the Chalk dips 

 throughout the greater part of its range from west to east, the 

 breadth of surface occupied by it is inconsiderable compared with 

 that of most of the strata above and below it, while, on the other 

 hand, its horizontal extension increases in proportion as the inclina- 

 tion of" the strata diminishes. For this reason, from Alum Bay to 

 Mottistone Down, and from Carisbrook to Cnher Cliff, lietween 

 which localities the Chalk is nearly vertical, it constitutes a mere 

 ridge of high land, scarcely a quarter of a mile broad in Afton 

 Down. Between Mottistone Down and Carisbrook, where the 

 strata become less inclined, the width of the band of Chalk 

 exceeds three miles. For the same reason, the outliers of Chalk 

 on the south side of the Island between St. Catherine's Down and 

 Shanklin Down, although of inconsiderable thickness compared 

 with th6 depth of the entire formation, yet in consequence of 

 being nearly horizontal extend over a comparatively wide surface. 

 Throughout the central range of the Island the dip of the Chalk 

 graduall}^ increases in amount towards its higher strata, becomino- 

 nearly vertica.1 at its junction with the overlying Tertiary formations. 



The well-known rocks called the Needles are large wedo-e- 

 shaped masses of Chalk standing out in the sea, isolated frqni the 

 main body of Chalk by the wasting action of the waves upon the 

 coast. A lofty spire of chalk, which once rose as the most con- 

 spicuous of the group and chiefly suggested the name to these 

 rocks, fell down in 1764. Conspicuous as they look from the 

 land, the Needles appear of much larger dimensions when viewed 

 from the sea. A base of 60 feet in diameter has been levelled on 

 one of them for the foundations of the lighthouse, which was 

 removed to it in 1858 from High Down, where it originally stood. 



Other masses of chalk, consisting of the lowest beds of the ilintv 

 Chalk, for in similar but smaller isolated I'ocks in the sea near the 

 base of the cliffs on the east side of Freshwater Bay. These are 

 shewn in the accompanying sketch, Fig. 15, by Prof Edward 

 Forbes, made in the year 1852, for his Memoir on the Tertiary 

 Fluvio-Marine Formation of the Isle of Wight (Fig. II., p. 4).'^ 



* These sea-stacks of Chalk seem to have undergone considerable diminution 

 since this sketch was made. 



