CHALK. 413 



ford, at Saffron Walden, near Bishop's Stortford/ and in the large 

 pits at Grays Thurrock. At Grays the thickness is upwards of 660 

 feet, and in a deep well at Harwich it was proved to be 8qo feet. 



In Middlesex the Chalk is exposed at Harefield, north of Ux- 

 bridge ; and it occurs at some depth beneath London ; at Kentish 

 Town its thickness was 645 feet, and at Meux's Brewery 655 feet.^ 

 (See Fig. 31, p. 202, and Fig. 70, p. 414.) 



In the deep boring at Richmond the following beds of Chalk 

 were passed through : ^ — 



Upper Chalk, { Chalk with flints. Zone of Micrasters (the Chalk with 

 300 feet. ( BdeinniteUas is not represented in the London area). 



^Chalk Kock. Zone of Holastcr plaints, 5 feet, 

 lu'^ 11 ri 11- Chalk with few and scattered flmts. Zones of Tc'rcbratiilina 

 r . \ gracilis una Jnocerai?iiis labiatus. 

 ^ ' I Melbourn Rock, and Zone of Belemiiitella plena. Nodular 



<w or conglomeratic chalk, about 15 feet. 



f t ' 1 ^^'^y marly Chalk without flints, and Chalk Marl. 



In Berkshire the thickness of the Chalk is much the same as 

 in Buckinghamshire and Oxfordshire ; the Chalk-rock being from 

 six to twelve feet thick. A fine section of Chalk Marl is exposed 

 on the Great Western Railway at Wallingford Road Station. Here 

 Ammonites Rothomagciisis, Turrilites iubeniilatus, Pecten Beavcri, 

 Inoci ramus mytiloidcs, etc., occur. The Upper Chalk is shown in 

 the Railway-cutting at Pangbourn; and at a Chalk-pit near Hart's 

 Old Lock, Upper Chalk, Chalk Rock, and Middle Chalk, were ex- 

 posed.^ Chalk is to be seen in the ice-house at Windsor Castle ; 

 while at Datchet it occurs at a depth of 117 feet from the surface. 

 (See Fig. 64, p. 385.) 



NORTH AND SOUTH DOWNS. 



The Chalk forms the North and South Downs, bordering the 

 Wealden district. It is well exposed in the cliffs at Gravesend, 

 Westgate-on-Sea, Margate, Broadstairs, and Ramsgate, and in 

 those extending from near Walmer Castle, south of Deal, by St. 

 Margaret's, the South Foreland, and Dover, to Shakespere's Cliff 

 and Abbot's Cliff, north of East Wear Bay, Folkestone ; to the 

 south it is exposed in the cliffs extending from Beachy Head and 

 Seaford to Brighton and Littlehampton. (See Figs. 57, 60, and 66.) 



The inclination of the Chalk along the North l3owns from Dover 

 to Guildford is from 10° to 15°; further west, at the Hog's Back, 

 it increases to upwards of 45°, and hence its outcrop is very 

 narrow in places. 



1 See Geol. N. W. part of Essex, etc., by W. Whitaker, W. H. Penninf^ 

 W. H. Dalton, and F. J. Bennett. '^' 



2 Whitaker, Mem. Geol. Survey, iv. 21 ; Geol. London, ed. 4, p. 20. A revised 

 edition of the Section Fig. 70, is published as a frontispiece to the last-named work. 



s J. W. Judd, Q.J. xL 731. 



* W. Whitaker in Explan. Sheet 13 (Geol. Survey), p. 18. 



