﻿Vol. 6 1.] PHOSPHATIC CHALK OF TAPLOW. 487 



to belong to a higher zone, the failure to detect them there is scarcely 

 surprising. 



Though the exact boundaries of the Phosphatic Series have still 

 to be defined, its lateral range in certain directions can be shown to 

 be small. Thus, along the higher part of the river-bluff which 

 extends northward from the site of the Lodge Pit, there are some 

 exposures of the normal type of Chalk, referable to the Micraster cor- 

 anguinnm-Zone, at distances ranging from a quarter to half a mile. 

 The largest, and most distant, of these, known as the Root-House 

 Pit, shows a fine section of the flinty beds, the top of which is 

 probably not more than 15 feet below the base of the Eocene. 



Near the railway-station, to the south-east, and at a distance of 

 five-eighths of a mile, a similar chalk, capped by a remnant of the 

 green, pebbly, ' bottom-bed ' of the Reading Series, is shown in a 

 pit worked for chalk and gravel. 1 Mr. Strahan, who notes the flinty 

 character of the beds in these exposures, records a similar rock (also 

 at the boundary of the Tertiary formations) seven-eighths of a mile to 

 the north-north-east, in a section now all but destroyed, and yielding 

 only chips of Inoceramus. On the south-west and north-east, the 

 nearest pits are 1 1 miles distant from the Lodge section and the Hill- 

 Parm cess-pit respectively, and show cor-anguinum-heds of the usual 

 type of the upper half of the zone, within a few feet of the junction 

 with the Eocene strata. To the westward, the phosphates are cut 

 off by the Thames Valley, while on the south and due eastwards 

 their lateral range is quite unknown, as in those directions they 

 are hidden, together with the rest of the Chalk, by thick sheets 

 of river-drift and by the main body of the Tertiary deposits. 



The incoming and disappearance of a mass of Marswpites- and 

 Micraster cor-anguinum-heds of exceptional character to a thickness 

 of at least 60 feet, between the normal cor-anguinum-Chalk and the 

 Reading Beds, within a distance not greater (and possibly much 

 less) than 1 mile along a roughly north-west to south-east line, 

 indicate the existence of a marked unconformity between the Cre- 

 taceous and the Eocene rocks in this district. It is clear that these 

 beds must either form a low boss, or eminence, rising above the early 



1 As Mr. Strahan has suggested (loc. cit.) that the chalk of this pit may 

 possibly overlie the ' phosphatic zone,' we append a list of the fossils obtained 

 from it by Mr. Rhodes (for the Geological Survey) and by ourselves : — 



Inoceramus Cuvieri, Sow. 



King en a lima, Defr. 

 xPectcn cretosus, Defr. 



Crania parisiensis (?) Defr. 

 *RhynchoneUa reedensis, Eth. 



Terebratulina striata, Wahl. 



Entalophora madre*poracea, Goldf. 



Entalophora virgula, Hag. 



Escharina inelegans, Lonsd. 

 * Membranipora arbor ea, d'Orb. 



Sparsicavea carantina, d'Orb. 



Bourgueticrinus ellipticus, Miller. 



* Indicates species in the Geological-Survey Collection 

 The above is clearly a Micraster cor-anguinum-Zox\Q assemblage. 



Cidaris clavigera, TCoenig. 

 Cidaris hirudo, Sorig. 

 Cidaris sceptrifera, Mant. 

 Echinocorys scutatus, Leske, var. 



ovatus. 

 Galerites albogalerus, Leske (forma 

 pyramidalis) (in a band). 

 *Metopastcr Parleinsoni, Forbes. 

 Nymphaster (?). 

 Pseudodiadema fragile, Wilts. 

 Porosphcera patelliformis, Hinde. 



