﻿492 MESSES. WHITE AND TREACHER ON THE [Aug. I905, 



In the present instance, however, rarity is a quality to which it 

 is easy to attach too much importance. When regarding the 

 Taplow phosphates as a whole, one instinctively contrasts them 

 with the normal Chalk of the adjoining country, and the dominant 

 impression received is that of their singularity. But it must be 

 remembered that they are of a different age from the rocks with 

 which they appear to be so intimately associated, and form a relic 

 of a sheet of newer beds once extending over the district. Although 

 the nature . of those vanished beds is not to be safely inferred from 

 the sample that remains, it is nevertheless open to question whether 

 the Taplow phosphates may not present a type of deposit which 

 was fairly common in the contemporary sediments of this part of 

 the country. In this connection, it is important to note that the 

 Phosphatic Chalks found at the same horizon, and at higher 

 horizons,, in the Upper Cretaceous rocks of Northern France and 

 Belgium, though nearly all, individually, of very limited extent, 

 commonly occur in groups scattered over tracts of country many 

 square miles in area. The Taplow example may well be a member 

 of such a group ; in which case other members may still exist in 

 the district — possibly beneath the main mass of the Eocene deposits 

 to the south and east. A complete demonstration of their absence 

 would not, necessarily, dispose of the possibility of their former 

 existence; for, on the supposition that the trough containing the only- 

 known example is due to folding, a plausible reason for the special 

 preservation of that deposit is at hand. The synclinal flexure 

 which carried it below the general level of the contemporary strata, 

 and placed it in its present anomalous position among older rocks, 

 also carried it below the plane which was subsequently adopted 

 as the downward limit of early Tertiary erosion. 



VI. Summary of Conclusions. 



(i) The Phosphatic Chalk of Taplow, exposed at the South Lodge 

 of Taplow Court, is referable to the zones of Micr aster cor-anguinum 

 and Marsupites testudinarius. 



(ii) The two, more richly-phosphatic, Brown Beds, distinguished 

 in the foregoing account by the letters (B) and (D), belong to the 

 latter zone, and represent the lower parts of the Uintacrinus-B'diid 

 and of the Marsujpites-Bajid, respectively, in a much attenuated 

 condition. 



(iii) The distribution, numerical proportion, and, to some extent, 

 also the morphological character of the macroscopic fossils of this 

 Chalk, are exceptional. 



(iv) A part, at least, of the phosphatized material entering into 

 the composition of the deposit has acquired its distinctive minera- 

 logical character on the spot. 



(v) So far as can be ascertained from existing data, the Phos- 

 phatic Chalk is confined to a small tract of country measuring less 

 than 3J miles from north-east to south-west, and less than 1 mile 

 from north-west to south-east. 



