﻿Vol. 6 1, j PHOSPHATIC CHALK OF XAPLOW. 465 



mass of the Tertiary strata of the London Basin comes on with an 

 extremely-irregular, drift-obscured boundary. 



The dominant south-eastward inclination of the solid rocks is 

 reflected in the prevailing surface-slope of the higher ground of the 

 neighbourhood, but their secondary tectonic features have little or 

 no definite topographical expression ; and, as will be shown in the 

 sequel, the internal structure of this piece of country is somewhat 

 less simple than outward appearances would suggest at first sight. 



Before dealing with the section and its faunal sequence in detail, 

 it will be advisable to quote the stratigraphical succession made 

 out by Mr. Strahan (Quart. Journ. Geol. Soc. vol. xlvii, 1891 , p. 356), 

 which we found useful as a guide during the earlier stages of our 

 examination : — 



Feet inches. 



(11) ' Soft white chalk, top not seen 12 



passing down into 

 (10) Brown chalk with Ostrea acutirostris, Miss., Belemnitella 

 quadrata, Defrance (both abundant), Echinocorys vul- 

 garis, Breyn., and Cidaris sceptrifera, Defrance [sic] about 8 

 (9) White chalk, traversed by numerous tubes and cavities 

 filled with brown chalk ; a hard and blocky top, form- 

 ing a marked floor to the brown chalk above 3 



(8) White chalk, mostly inaccessible, and not examined in 



detail 14 



(7) White chalk with scattered brown grains 2 6 



passing down into 



(6) Brown chalk about 4 



(5) Hard crystalline chalk, with nodular structure and 



greenish markings (like Chalk-Bock) about 1 



(4) White chalk, piped with brown chalk, as above 1 10 



(3) A sandy brown layer 0£ 



(2) White chalk, piped with brown chalk 2 6 



(1) White chalk to the bottom of the pit, the first flints 

 occurring 12 feet below the lower band of brown 

 chalk 15 0+' 



[The numbers in parentheses have been attached by us to facilitate reference.] 



Our reading of the section differs in some respects from the 

 above. The divergence is, no doubt, mainly attributable to the 

 broader character of the present investigation, Mr. Strahan having, 

 apparently, devoted his attention almost entirely to the smaller 

 lithological features of the rich phosphatic bands. The more im- 

 portant points on which we differ from him will be noted as they 

 arise. 



We find it convenient to divide the section into five parts, as 

 follows : — 



Feet. 



E. Upper White Chalk (11) visible 16 



D. Upper Brown Chalk, or rich phosphatic band (10) ... about 8 



C. Middle White Chalk (9, 8, 7) about 16 



B. Lower Brown Chalk, or rich phosphatic band (6) ... about 4 



A. Lower White Chalk (5, 4, 3, 2, 1)" visible 17 



[The numbers in parentheses indicate the equivalent beds in Mr. Strahan's 

 succession.] 



Q. J. G. S. No. 243. 2 l 



