"Vol. 52.] WITH HOLASTER PLANUS AT LEWES. 465- 



The whole exposure therefore ranges from the Mici'aster-zonus 

 of the Upper Chalk to the Rhynclionella Cuvieri-zone of the Middle 

 Chalk inclusive, and the brown chalk may be referred with certainty 

 to the horizon of the Chalk Rock. In this respect alone it differs 

 from the phosphatic chalk of Taplow, which occurred in the zone 

 of Belemnitella quadrata, 20 feet only below the base of the 

 Tertiary deposits of that neighbourhood. 



The Southerham phosphatic chalk resembles that of Taplow so 

 closely in composition that its description may be dismissed in a 

 few words. It consists of a white chalky matrix in which are- 

 embedded a multitude of brown grains. In weathered specimens 

 these grains can be washed out in water, but the separation can be 

 better effected by dilute acetic acid, which removes almost all the 

 matrix, but scarcely corrodes the brown grains. Mr. Player, to 

 whom I was indebted for the chemical examination of the Taplow 

 Chalk, confirmed my opinion that the brown grains from Southerham 

 also consist largely of phosphate of lime. They resemble those of 

 the Taplow 7 Chalk so nearly that he did not consider it necessary to 

 make a full analysis. The Taplow grains were found by him to 

 contain 50*6 per cent, of phosphate of lime, while the rock in its 

 raw state contained 18 to 35 per cent. 1 The Southerham brown 

 chalk in the raw state is probably rather less rich than the Taplow 

 material, and this, taken in connexion with the fact that it is 

 thin and impersistent, seems likely to preclude it from proving of 

 economic value. 



The microscope also shows a complete resemblance between the 

 residue of the Southerham and Taplow chalks, after treatment with 

 acetic acid. In the former the oval pellets which were determined 

 as the coprolites of small fishes are rather more abundant and larger, 

 but proportionate in size to the numerous teeth which occur. The 

 prisms of Inoceramus-shell are rather less common, but internal 

 casts of foraminifera form a large proportion of the residues, and 

 small amber-coloured chips of bone occur equally in both. A thin 

 slice of the raw rock shows the clear shells of the foraminifera 

 surrounding the internal phosphatic casts. 2 The reactions with 

 polarized light are the same in both rocks. When treated with 

 hydrochloric acid some of the foraminifera are seen to have been 

 filled with a greenish mineral resembling glauconite, the proportion 

 so filled being rather larger in the Southerham than in the 

 Taplow Chalk, especially in the greenish nodules which occur in 

 the phosphatic band. Further details of either chemical or micro- 

 scopical examination of the rock would be a mere repetition of the 

 account of the Taplow Chalk given in this Journal (vol. xlvii. 1891, 

 pp. 358-362). 



The flint referred to in the third section as occurring 2 inches 

 above the rocky floor is seen under the microscope to contain many 



1 Quart Journ. Geol. Soc. vol. xlvii. (1891) p. 358. 



2 PI. xx. fig. 2 in 'Deep Sea Deposits' {Challenger Reports) shows recent 

 foraminifera from a depth of 1900 fathoms similarly infiltrated. The illustra- 

 tion closely represents the appearance of the organisms of the phosphatic chalks 



