330 



ME. A. STRAHAN ON A PnOSPHATIC 



21. On a Phosphatic Chalk with Belemnitella quadrata at 

 Taploav. By A. Stkahan, Esq., M.A., F.G.8. (Bead March 25, 

 1891.) 



[Communicated by permission of the Director-General of theGeological Survey.] 



While engaged in the course of my duties in arranging the 

 specimens collected for the Bock Collection in the Museum of 

 Practical Geology, my attention was attracted hy a chalk of unusual 

 character. The specimen was collected by John Bhodes, when the 

 second edition of the " Geology of London " (Memoirs of the Geological 

 Survey) w^as in preparation, from an old pit at the Lodge of Taplow 

 Court, the seat of W. H. Grenfell, Esq. By j^ermission of the 

 Director-General, I examined the pit, and made the following 

 descending section : — 



Lodge Pit, Taplow Courts 



ft. in. 

 Soft white chalk, top not seen \'l 



passing down into 

 Brown chalk with Ostrea aciitirodris, Nilss., Belemnitella quadrata, 



Defrance (both abundant), Echhiocorys vulgaris, Breyn., and 



Cidaris sceptrifcra, Defrance, about 8 



White chalk traversed by numerous tubes and cavities filled with 



brown chalk ; a hard and blocky top, forming a marked floor to 



the brown clialk above o 



Wliite chalk, mostly inaccessible, and not examined in detail 14 



White chalk with scattered brown grains 2 6 



passing down into 



Brown chalk, about 4 



Hard crystalline chalk with nodular structure and greenish 



markings (like Chalk Rock), about 1 



White chalk, piped with brown chalk as above 1 10 



A sandy brown layer 0^ 



White chalk, piped with brown chalk 2 (5 



White chalk to the bottom of the pit, the first flints occurring 



12 feet below the lower band of brown chalk 15 ()-(- 



At the top of the pit there occurs a thin streak of intermingled 

 red clay and green sand, Avith a few green-coated flints, which has 

 clearly been washed but a few feet down from the Tertiary outlier 

 on which Taplow is situated. The true base of the Tertiary strata 

 lies probably not more than 10 feet above the highest chalk seen in 

 the pit. The dip in the pit and along the hillside northwards is 

 about E. 10° S. at 4° or 5°. In the memoir referred to (vol. i. 

 p. 77) a correlation of this chalk with the well-known Margate 

 Chalk, or the zone of Marsvintes, is suggested on the evidence of 

 the occurrence of Belemnitella quadrata and the scarcity of flints. 

 The total thickness of Upper Chalk existing in the neighbourhood is 

 believed to be between 250 and 300 feet. 



[A shaft, which has been sunk in the hillside above the pit since 

 the reading of this paper, gives the exact depth of the phosphatic 



