CHALK WITH BELEMNITELLA QUADRATA. 361 



the concentration of the pliosphatc was primarily due to the action 

 of tishcs, the pliosphatization of the other organisms in the rock 

 having resuUcd from the replacement, more or less complete, of 

 carbonate hy phosphate of lime. Tlie sharpness of the outline and 

 the invariably fragmentary condition of tlie fish-bones suggest that 

 they have undergone mastication by an animal possessed of grinding 

 teeth. 



Large fragments of a Beh-mmtella and of an Inoceramus from the 

 brown chalk, crushed and examined under the microscope, showed 

 the optical properties of carbonate of lime, the prisms of the latter 

 being readily distinguishable from those which are scattered through 

 the brown chalk, Neither the Beleuinkella nor the Inoceramus Qiwe 

 a precipitate with ammonium molybdate. A fragmeufc of an 

 Inoceramus from the greyish chalk between the two brown bands 

 yielded, when crushed, a number of prisms consisting of calcito, and 

 on treatment with hydrochloric acid left a large residue of silica *. 

 A specimen of Echinocor>/s from the brown chalk consisted of 

 calcite. From these observations I infer that the phosphate of lime 

 is confined to the foraminifera and to the small organic remains 

 embedded with them. 



It seems from the examination of the residue from acetic acid 

 that the tests as well as the contents of the foraminifera have 

 been phosphatized. In the tests the phosphate is translucent and 

 possibly in a crystalline condition, though, from its extremely low 

 double refraction, it does not display the black cross so conspicuously 

 as the carbonate of lime. In the interior of the chambers, on the 

 other hand, the phosphate has always taken an opa(]ue form corre- 

 sponding perhaps to that of the matter it has replaced, though it 

 should be noted that many of the chambers of the non-phosphatized 

 foraminifera are, and probably have always been, empty. In the 

 case of the prisms the whole of the phosphate seems to be in an 

 opaque form. 



Tlie effect of calcining the brown grains in a closed crucible at a 

 low red heat is to blacken them all over ; raised to a white heat they 

 become white, or nearly so. When tested with phenol phthaleVn, 

 which has the property of turning red in the presence of an alkali, 

 the calcined grains are attacked unequally. Some assume a pink 

 colour at once, others after several minutes, while a few, and among 

 them many of the amber- coloured chips, show no coloration. 

 Those which turn red are permeated by the colour in a manner 

 which seems to indicate the presence of quicklime in every part of 

 the grain t- This tends to confirm the inference, drawn from the 

 behaviour of the grains when under treatment with acetic acid, that 



* A section made transversely to the prisms by Mr. Dick shows that the 

 prismatic structure is entirely wanting in the siUceuus portion of the fragment. 

 The boundaries of the siliceous portion, moreover, cut across the walls of the 

 prisms without the slightest tendency to follow them. The silica is doubly 

 refracting. 



t I am indebted to Mr. Player for suggesting this experiment. 



Q.J. G. S. No. 187. 2 c 



