﻿Vol. 6 1.] PHOSPHATIC CHALK OP TAPLOW. 467 



The first signs of phosphatic material were observed a few 

 inches below the tabular flint-seam. At that horizon small, 

 scattered fish-remains, coprolites, and rare phosphatized foraminifera 

 become noticeable ; and with them are associated a few dull, 

 yellowish-brown, subangular phosphatic concretions, from a sixteenth 

 to a quarter of an inch in diameter, with minute crevices or perfor- 

 ations, and chalky inclusions. These materials disappear and recur 

 throughout the higher beds of this division, but their distribution is 

 too irregular to allow of their being referred to definite bands. 



At about 6 feet above the flints (or 8 feet from the top of this 

 chalk) polished brown granules, consisting of the small phosphatized 

 organic matter just mentioned, but with a much larger proportion 

 of foraminifera, and identical with those forming upwards of 60 

 per cent, of much of the overlying Brown Chalk, appear in bunches 

 in an iron-stained paste filling ill-defined tubes or ' borings ' ; and 

 within the next 2 or 3 feet similar granule-filled tubes come in 

 abundantly, their number increasing, but by no means steadily, 

 as the summit of this division is approached. These borings are, 

 broadly speaking, of two types : (1) the sharply-defined, sub- 

 cylindrical, and branching, and (2) the vague, irregular, and digitate ; 

 but many intermediate forms exist. Despite the existence of such 

 passage-forms, we are not satisfied that the contents of the vaguer 

 sort are due, in every case, to intromission from above. Here, and 

 also in the other white chalks of the section, the localization of the 

 brown granules is often more suggestive of some process of segrega- 

 tion, or, at least, of development along certain paths. The more 

 regular borings (from J to 1 inch in diameter) of the Taplow Chalk 

 do not exhibit the curious ridging at the junction of stem and 

 branch to be seen in their analogues in the Chalk-Rock of Lewes 

 and elsewhere. They are best developed in the higher beds of this 

 division, and there they often contain the phosphatized casts of 

 sponge-stems and the glazed nodules which characterize the lower 

 portions of the overlying Brown Chalk. 



In the higher beds, also, spherical and vermiform concretions of 

 dark red iron-peroxide (decomposed pyrite) are of rather frequent 

 occurrence. 



We have not observed a definite bed exhibiting the character and 

 occupying the position of Mr. Strahan's half-inch ' sandy brown 

 layer' (numbered 3); but there are many impersistent seams of such 

 sandy material, up to 3 or 4 inches in thickness, following curved 

 and rectangular joints, or fissures, in the higher beds. These seams 

 consist very largely of phosphatic granules, with little or no chalky 

 investment, and the presence of quartz-grains, brown clay, carbon- 

 aceous matter, and rootlets of trees, shows them to be merely the 

 result of the mechanical and chemical action of atmospheric water 

 percolating through the overlying rich phosphatic bands. 



Mr. Strahan's description of the rocky layer (5) capping the 

 lower white beds, as ' a hard crystalline chalk, with nodular structure 

 and greenish markings (like Chalk-Rock),' is sufficient for most 

 purposes, but needs some amplification here. For, in this bed, there 



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