CHALK WITH BKLEMNITELLA QUADRATA. 3G3 



on the whole larger and darker than those in the Taplow Chalk, but 

 they consist of toraniinifera, prisms of Inoceramiis-shcil, bone- 

 fragments, and oval pellets, and in all essential points the two 

 deposits are identical. After treatment with acetic acid this chalk 

 furnishes remarkably beautiful specimens of phosphatized organisms, 

 and occasionally gives examples of internal casts in phosphate of 

 lime of foraminifera (principally Planorhulina) with hair-like casts 

 of the perforations in the test adhering. 



M. Lasne notices that the proportions of fluoride of calcium and 

 phosphoric acid are in the relation of 1 to 3 : that is, in the same 

 proportion as in apatite, from which he concludes that the mineral 

 is a fluophosphate rather than a phosphate. The fluophosphate, as 

 he terms it, is worked for commercial purposes in pockets of great 

 size and depth, which it lines, generally speaking, up to the level of, 

 but not above, the grey phosphatic chalk. The concentration of 

 the mineral in these pockets has doubtless been due to the action 

 of soil- water, as has been the case at Ciply in Belgium. 



Scarcely less striking is the resemblance of the Taplow Chalk 

 with that of Ciply, from which large quantities of phosphate of 

 lime are being extracted. Though the Ciply Chalk lies above the 

 zone of BeJemniteUa mucronata^ and above the highest zone recog- 

 nized in England, the close similarity of the two rocks merits 

 more than a passing mention, especially in view of the possibility 

 of the Taplow deposit proving to be of commercial value. The 

 Belgian phosphatic beds were described before this Society in 1886 

 by M. Cornet *. They were first worked in 1870, and yielded 85,000 

 tons of phosphate of lime in 1884. Above the phosphatic chalk lies 

 a tufaceous deposit {Tuffeau de Cijily), with a conglomerate at its 

 base {Foudingue de la Mcdogne) which has been shown by MM. 

 Rutot and Yan den Broeck to be of Tertiary age f. The phosphatic 

 zone includes 20 to 30 feet of coarse chalk with grey flints, which 

 passes down into a chalk of greyish brown colour, with phosphate 

 of lime in small brown grains. This in turn shades down into a 

 phosphatic chalk with numerous flints, which becomes less rich 

 downwards, until it passes into a rock formed entirely of carbonate 

 of lime. The whole rests upon the white chalk of JN^ouvelles, which 

 corresponds to the Chalk of Meudon, or the upper part of the zone 

 of BelemniteUa mucronata. The Meudon Chalk is correlated with 

 the jSTorwich Chalk of England by M. Hebert. The greyish 

 brown phosjjhatic chalk has the following composition according 

 to M. A. Petermann, Director of the Agricultural Station of 

 Gembloux t. I insert Mr. Player's figures here to facilitate 

 comparison : — 



* Quart. Journ. Geol. Soc. toI. slii. p. 325. 



t Geol. Mag. (188(i) p. 10. 



X Bull. Acad. Roy. Belgique, 2">*^ ser. t. xxxix. (1875) p. 25. 



