362 MR. A. STRAHAN ON A PHOSPHATIC 



the phosphate and carbonate of lime composing them are intimately 

 mixed. 



(4) Lastly, when the residue from acetic acid is treated with 

 hydrochloric acid, a large proportion is dissolved, including all the 

 phosphate of lime, part dissolving with effervescence and part 

 without. The residue from cold dilute hydrochloric acid consists, 

 in the case of a rich brown specimen of the chalk, of a number of 

 rust-coloured grains. Hot concentrated hydrochloric acid removes 

 this colour, and becomes itself amber-coloured, at the same time 

 evolving a bituminous smell. There remains a small number of 

 solid, dull greenish grains, the internal casts of foraminifera, and a 

 larger number of pellicles presenting the shapes of foraminifera in 

 a skeleton form. The solid casts, pressed between two glasses, be- 

 have like gelatinous bodies. 



The Taplow Chalk bears a strong resemblance to a phosphatic 

 chalk which is worked in the north of France, at Beauval, near 

 Doullens, and Hallencourt (Somme), Hardivilliers (Oise), and at 

 Briastre and Quievy (Nord). This phosphatic zone contains Belem- 

 nitella quadrata^ and lies some 30 feet above the zone of Micraster 

 cor-testudinarium. It may therefore be attributed to the zone of 

 Marsupites (with which, moreover, it contains several fossils in 

 common) * : that is, to the same horizon approximately as the 

 Taplow Chalk. The Doullens deposits have been described by 

 M. H. Lasne, from whose paper the following notes are ab- 

 stracted t. The strata occur in descending sequence as below : — 



Soft white chalk with flints. 



Grey chalk with Belemnitella quadrata, with a little nodular band of rich 



phosphate at its base, 20 to 80 feet. 

 Soft white chalk without flints, occupying the position of the zone of 



Micraster cor-anguinum, about 30 feet. 

 Chalk (zone of Micraster cor-testudinarium) , hard and nodular below, and 



with many bands of flints, about 60 feet. 



The grey chalk, according to M. Lasne, consists of a white paste, 

 with a multitude of little grains of brown phosphate of lime, all of 

 which are derived from small organisms. M. Stanislas Meunier has 

 shown that they are formed of an envelope of crystalline phosphates 

 of radiate structure, generally enclosing a core of pulverulent chalk. 

 GJohif/erina, Teoctidaria^ Cristellaria, and Rotalia all occur, together 

 with some small cylindrical and rod- like bodies. 



By the kindness of M. Stanis;las Meunier I have been furnished 

 with a specimen of the Beauval phosphatic chalk. The grains are 



* Belemnitella quadrata, Defrance, Bhynckonella pKcatilis, Sow. (var. octo- 

 plicata), R. lirnbata, Schloth., Echinocorys {Ananchytes) vidgaris, Breyn., Cur- 

 diastcr {Holaster) pillula, Ag., are common to the Grey Chalk of Doullens and 

 the Marsupites-zowQ of Wells (Norfolk). The reptiles and fishes of the Doullens 

 Chalk show a closer affinity with the Norwich Chalk, which lies above the 

 Marsupites zone. 



t ' Sur les Terrains phosphates des environs de Doullens, Etage S6nonien et 

 Terrains superposes,' Bull. Soc. Geol. France, 3'"^ ser. t. xviii. (1890) p. 441. 



