UPPER AND LOWER CHALK OF DOVER, ETC. 245 



shows the chalk beneath, a marl band usually marks the commence- 

 ment of a somewhat rapid passage from the softer chalk to the hard 

 rock (fig. 3). The chalk below the rock appeared uufossiliferous, but 

 Gasteropods, a few Micrasters, and other fossils may be found on tha 

 top of the rock. Everywhere overlying it there is white chalk con- 

 taining hard crystalline lumps, and at Henley I noticed these shomng 

 some aiTangement in layers. This kind of chalk may be traced for 

 from 15 to 20 feet ; it is fossiliferous and contains flints scattered 

 and also arranged in rather indefinite lines. 



At Aston and Chinnor are two good sections in which the Chalk 

 Hock is exposed. Overlying it is the fossiliferous chalk with hard 

 lumps. Micr asters are abundant ; Jlicraster cor-testudinarium is 

 associated with M. hreviporus, Echinocorys vulgaris^ Ammonites 

 peramplus, Gasteropods, &c. About 20 feet above the Chalk Rock 

 with the green-coated nodules like that seen at Henley is a second 

 hard yellowish band, which is not nodular and very much like the 

 hard upper yellowish rock of Dover. Flints in regular lines and one 

 layer of tabular flint can be seen in the white chalk above the 

 yellow rock (fig. 3). 



But the " Chalk Eock" is not always compact as at Henley. Mr. 

 Whitaker describes that seen south of "Wycombe-Marsh Station (?) 

 as " irregular in structure, not hard throughout, beds of cream- 

 coloured rock with nodules alternating in fact with beds of chalk.'" 

 Again at Jenkin's Hill " There are two bands of rock 12 feet apart ; 

 chalk without flints occurs below, chalk with flints above." And at 

 Valenciennes Parm he records a section showing 3 layers of more or 

 less defined Chalk Rock in about 10 feet, and above this there is 

 "nodular yellow-stained chalk," tabular flint occurring beneath this. 



At Prince's Risboro the Chalk Rock is shown in beds each with a 

 definite line at top, the chalk passing up rapidly with deepening 

 yellowish tint to hard rock, as at Dover, which ends abruptly, softer 

 chalk overlying it. In Hertfordshire similar sections occur ; but here 

 the character of the rock is slightly altered, the green-coated nodules 

 are not so evident, and it is frequently broken up into lumps with 

 softer " mealy " chalk between them. In the Cambridge Memoir 

 the rock is described at an exposure near Abington Park as " an irre- 

 gular layer of rubbly, crystalline, yellowish chalk in lumps enclosed 

 in a marly matrix," &c. ; and N."W. of Westley as '^ hard chalk with 

 several yellowish layers near the base, containing lumps of hard 

 crystalline chalk," (fee. The green-coated nodules are not noticed 

 here at all. 



Taking aU the evidence into consideration, and including Dover, 

 I come to the following conclusions, viz. :— (1) That there exists in 

 the Chalk at a certain horizon above the base of the Melhoum Rock 

 (not less than 220 feet in the localities mentioned herein) rocky 

 bands, probably not all persistent, to which the name "Chalk Rock" 

 may be applied ; (2) That the rock seen at Henley, the characters 

 of which are persistent over a large area, is one of these bands ; 

 (3) That these bands do not necessarily mark a palaeontological 

 horizon. 



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