﻿Vol. 6 1.] PHOSPHATIC CHALK OF TAPLOW. 475 



A group of fin-bones of a fish, about 6 inches in length ; fish- 

 teeth with fragments of bone attached ; and small carbon-lined 

 cavities of angular section (=wood?) are among the objects 

 collected from this division. 



It should here be noted that the tests for phosphorus, in the larger 

 fossils of the brown chalks of Taplow, applied by Mr. Strahan were 

 not sufficiently exhaustive to justify the important inference that 

 the phosphate of lime in those beds ' is confined to the foraminifera 

 and to the small organic remains embedded with them.' 1 Apart 

 from the concretions present at most levels, and the obviously- 

 phospha.tized sponges, Micrasters, Sjooiidyli, Plicalulce, Serjmlce, etc. 

 occurring in the Lower Brown Band (which that author seems to have 

 overlooked), a rather large proportion of the macroscopic fossils in 

 both brown bands gives evidence of phosphatic impregnation. Some 

 of the larger remains, such as those of Ostrea, Inoceramus, and 

 Actinocamaos (outer layers of guard), which, by reason of their 

 tenuity, or lamellar or prismatic structure, are more readily 

 penetrable, often give the characteristic reaction with ammonium- 

 molybdate after repeated and destructive cleansing with strong acids, 

 and continue to do so until entirely destroyed. Others, of more homo- 

 geneous character— as, for instance, plates of Cidaris, Echinocorys, 

 and Marsupites — usually cease to react at an early stage in the 

 process, showing the impregnation to have extended, in their case, 

 but little below the surface; and, while it is true that there arc 

 many instances in which the samples do not respond to this delicate 

 test, after the preliminary treatment for the removal of the visible 

 adherent granules of the matrix, it is equally true that no well- 

 represented class of organic material collected by us is wholly 

 exempt from this impregnation. 



The finest washings of the white or yellowish chalky paste of the 

 brown chalks are rarely or never free from phosphorus. 



Division (E). 



The Upper White Chalk is much obscured, and rather difficult of 

 access. It is, as a whole, fine, white, and rather closely jointed. 

 Soft in its lower parts, it becomes firm and lumpy higher up, and 

 in the topmost 3 or 4 feet is very hard, and often of a semi- 

 crystalline, horny, or porcellanous aspect, the detached blocks 

 weathering into a nodular rubble at the base of the overlying 

 •drift. In these hard beds there is a noticeable recrudescence of 

 dendritic manganese-dioxide. Save in this respect, and in that of 

 their hardness, however, they do not resemble the rocky layers at 

 the top of the preceding White Chalks (A & C). 



Granules of brown phosphate of the usual types, and anastomosing 

 tubules (or borings) containing the same material, are very numerous 

 in the lower 4 feet, gradually decreasing upwards. The borings 

 become very ill-defined as the hard beds are approached, and are 



1 Quart, Journ. Geol. Soc. vol. xlvii (1891) p. 361. 



