Tol. 52.] PHOSPHATIC CHALK AT LEWES. 463 



26. On a Phosphatic Chalk with Holaster planus at Lewes. By 

 A. Strahan, Esq., M.A., E.G.S. With an Appendix on the 

 Foraminifera and Ostracoda. By F. Chapman, Esq., A.L.S., 

 E.R.M.S. (Communicated by permission of the Director- 

 General of H.M. Geological Survey. Eead March 25th, 1896.) 



In 1891 I described before this Society a phosphatic chalk which 

 occurred near the top of the Upper Chalk of Taplow, and resembled 

 the deposits long known and worked in Belgium and the North of 

 France, but not up to that time recognized in this country. 1 Up to 

 the present, in spite of much searching, no other occurrence of this 

 rock has been recorded in England, but during the summer of 1895 

 Mr. John Rhodes, fossil collector to the Geological Survey, while 

 engaged in collecting from the great chalk-pits near Lewes, noticed 

 a thin band bearing a strong resemblance to the Taplow phosphatic 

 chalk. At the request of the Director-General I visited the spot 

 and made the following notes. 



The pit, which is marked on the 6-inch and 1-inch (new series) 

 Ordnance maps as the Southerham Pit, lies on the south-western 

 side of the high downs of Upper Chalk which overlook Lewes from 

 the east. A somewhat marked syncline traverses the central part 

 of these hills in an east-and-west direction. Thus Lewes, situated 

 nearly on the synclinal axis, stands on Upper Chalk, but both to 

 the north and south of the Downs the Middle and Lower Chalk 

 emerge with southerly and northerly dips respectively. The 

 Southerham Pit extends from the Middle to high up in the Upper 

 Chalk, but the workings in the Middle Chalk have been abandoned 

 and are partly obscured. A small bank, however, at the eastern end 

 of the long line of limekilns affords a good view of the junction of 

 the Upper and Middle subdivisions and of the phosphatic band in 

 question. Though only about 20 yards in length, the cutting suffices 

 to show the impersistent character of the deposit. To illustrate 

 this I give three sections taken at intervals of about 10 yards. 



About the middle of the Cutting. 



Massive chalk with flints. ft. ins. 



Flaky white chalk with a few flints and Holaster planus ... 4 

 passing down into 



Phosphatic chalk with many small fish-teeth, a few spines of 

 Cidaris and some nodules, partly green, partly brown, up 



to 1^ inch in diameter 1 6 



A sharp line of demarcation. 



Hard creamy limestone with calcite in veins and cavities, 

 nodular (some of the nodules being green-coated), lumps of 

 decomposed iron-pyrites 1 6 



Hard, white, compact chalk, traversed by branching pipes and 



thin laminae of phosphatic chalk 3 



Hard, white, compact chalk, with the pipes and laminae of 



phosphatic chalk less abundant and dying away downward. 3 



1 Quart. Journ. Geol. Soc. vol. xlvii. (1 891) p. 356 ; see also ' Natural Science,' 

 vol. i. no. 4, p. 284, and Geol. Mag. 1895, p. 336. 



