﻿484 MESSES. WHITE AND TEEACHER OJST THE [Aug. I905,. 



The detection of the concretionary variety of phosphate here may 

 not involve the rejection of the hypothesis * that the phosphatization 

 of the foraminifera and other small organic remains, which form a 

 large proportion of the brown granules of the Taplow Chalk, was 

 performed elsewhere, but it greatly reduces its probability. With 

 the striking evidence of the formation of calcium-phosphate on 

 the spot before one, there seems little need for the supposition that 

 those objects were imported, in their present condition, from some 

 more or less distant and unknown source. Moreover, the principal 

 argument in favour of that hypothesis, namely, the limitation of the 

 phosphate to the foraminifera, and to the other micro-organisms 

 associated with them, is shown, by more extended observation, to 

 be not entirely in accordance with the facts : some of the larger 

 fossils at certain horizons, and an appreciable, if small, proportion 

 of the body of the Chalk at almost all horizons, having clearly 

 undergone the same kind of alteration as the smaller organic debris 

 of the brown granules. 



Upholders of the derivation-hypothesis may, perhaps, find a new 

 weapon in the marked difference presented by the phosphatized and 

 the calcareous foraminifera of the White Chalks (C) and (E) into 

 which the brown bands graduate upwards. Those which are partly 

 or completely infilled or pseudomorphosed by phosphate are in 

 better preservation, include a larger selection of species, and con- 

 tain, in abundance, certain families (notably the Textulariidse and 

 Globigerinidse) which are rare in the calcareous examples. It is very 

 doubtful, however, whether this distinction existed at the time when 

 the beds in question were laid down : whether, in fact, it may not 

 be attributable to the relative indestructibility of the phosphatized 

 forms, which, as M. Cayeux has shown, 2 survive those common but 

 obscure structural changes in the Chalk that suffice to obliterate 

 all but the stoutest of the unaltered individuals. In the white 

 beds referred to we note that the calcareous foraminifera are 

 mainly such resistant forms of Rotalidse as occur in most micro- 

 scopic preparations of the Upper Chalk. 



The richness of the Taplow deposits in individuals and in species 

 of foraminifera is well known, but the possibility that its superiority 

 in these respects over most ordinary Chalks of about the same age 

 may not be altogether an inherent quality, seems to have escaped 

 recognition. If, as M. Cayeux insists (loc. cit.\ the Phosphatic 

 Chalks give a truer idea of the original character of the rhizopod- 

 fauna of the normal Chalk than can be gained b) ? a study of the 

 latter itself, the assemblage observed in the Taplow Chalk may be 

 regarded rather as typical than accidental, and its mixed deep- 

 and shallow-water character as possessing a wider significance than 

 has hitherto been attached to it. 



Among the many striking features of this Chalk there are, doubt- 

 less, some which plainly testify to the bathymetrical conditions 



1 A. Strahan, ' Natural Science ' vol. i (1892) p. 286. See also Eenard & 

 Cornet, Bull. Acad. Roy. Belg. ser. 3, vol. xxi (1891) pp. 153-58. 



2 Mem. Soc. Geol. du Nord, vol. iv, 2 (1897) pp. 322-23. 



