﻿Vol. 6 1.] rHOSPHATIC CHALK OP TAPLOW. 477 



The discovery of a gasteropod referable to the genus Scalaria, at 

 this horizon of the English Upper Chalk, is believed to be unique. 

 The fossil is represented by a portion of an internal cast, with 

 small pieces of the shell adhering to it. Mr. Jukes-Browne, who has 

 been so good as to examine the specimen for us, believes it to be a 

 relic of Scalaria decorata, Ecemer (1841) = Fasus costatostriatus, 

 Minister, in Goldf. ' Petref. Germ.' vol. iii, p. 23, & pi. clxxi, fig. 18 

 (1843) = Scalaria fasciata, Etheridge, 'Geol. of Cambridge,' Mem. 

 Geol. Surv. (Pal. Appendix) 1881, p. 140 & pi. i, fig. 1. 



Here, as in the lower divisions, Porosphcera globularis is quite 

 small. 



Above the Chalk, at the highest part of the section, there is a 

 degraded relic of the mottled clays and greenish ' bottom-bed ' of 

 the Reading Series (r, fig. 1, p. 466) ; and to the east and west of 

 this a wash of sand and gravelly loam (g) follows the slopes of the 

 spur in which the pit is excavated. 



The rudely- conical pipe of sandy clay and gravel (p), near the 

 middle of the section, possesses, in its lower part, a thick selvage of 

 brown phosphatic sand, and forms, we believe, the only-known 

 English analogue of the valuable poches de sable phosphate 

 of Belgium and Northern France. 



III. CoPvRELATION OP THE BEDS. 



It will be gathered from the foregoing description that the 

 greater part of the beds in this section are referable to the zone 

 of Marsupites testudinarius. 



The uneven upper surface of the rock-bed which caps Division (A) 

 may, with much probability, be regarded as the base of that zone. 

 Immediately above this surface we have the conglomeratic, nodule- 

 bearing, brown chalk with remains of Uintacrinus, Marsupites, and 

 Actinocamax verus ; below it, an unbroken sequence of white beds 

 which, since they contain Galerites albogalerus, and high-zonal forms 

 of Micraster, 1 and have so far yielded no fossil distinctive of the 

 Marsupites-Zone, may be referred to the upper part of the zone 

 of Micraster cor-anguinum. 



The Micraster cor-anguinum-Beds. — Though the fossils 

 in the Lower White Chalk (A) do not enable us to determine its 

 precise position in the M. cor-angui?mm-Zone, and the signs of 

 erosion at its junction with the Uintacrinus-'bea.ruig beds above 

 discount, in a measure, the value of the evidence from superposition, 

 there can be but little doubt that it belongs to the highest part of 

 that zone. For, if the fossils have little or no general value as 

 subzonal guides, they serve at least to distinguish this White Chalk 

 from the cor-anguinum-be&s exposed in other sections in this 

 district, which in no instance show the same assemblage of forms, 



1 A. W. Rowe, ' An Analysis of the Genus Micraster, &c.' Quart. Joum. 

 Geol. Soc. vol. lv (1899) pp. 494 et segq. 



