C. p. Chaticin 4" T. H. Withers— Chalk Section at Marlow. 123 



Ked River to the coast miist have been enormous, and has obviously 

 •contributed to the buikling up of the aggressive dune sands of this 

 district. 



The mineral composition of the sand of St. Ives Bay thus affords 

 a good example of the influence of the human factor in geological 

 pi'ocesses. 



YIII. — On the Chalk Skction at the Waterworks Quauuv, Mablow. 

 By Charles P. Chatwin & Thomas H. "Withers. 



HAVING had occasion to work at the Chalk Eock in this quarry, 

 Tve took advantage of the opportunity to examine the whole 

 of the Chalk exposed above that bed, which, owing to the inaccessibility 

 of the upper half of the quarry, had not been examined in detail. 

 The floor of the quarry coincides in part with the top of the Chalk 

 Rock, and as there is a vertical face of nearly 50 feet of Chalk above 

 it, the junction of the zones of Holaster planus and Jlicraster cor- 

 testudinarium was to be expected in the upper portion of the section, 

 and it was with the object of defining the junction of these two zones 

 that we paid attention to the higher beds. 



It was found possible, with the aid of a ladder, to collect from the 

 upperhalf of the quarry and to determine the zonal junction, and owing 

 to the interest attached to the finding of the Ammonite described in 

 the preceding paper (see February Number, p. 66), this seems a fitting- 

 opportunity to give a complete description of the section. The first 

 description was given in the Survey Memoir,' in which the Chalk was 

 assigned to the lower part of the Micraster cor-testudinarium zone. 

 In a later publication - the beds were described as belonging to the 

 upper part of the same zone. Later, Messrs. L. Treacher & H. J. 

 Osborne White ^ correctly referred the lower part of the quarrj- to the 

 iione of Holader planus, and the higher beds to that of Micraster 

 ■cor-testiiditiariiim, but were unable to obtain sufficient evidence to fix 

 the junction of the two zones. They further state that the floor 

 in part coincides with the top of the Chalk Rock, but record no fossils 

 from that bed. A long stretch of Chalk is exposed in the quarry, and 

 it is probable that the descriptions by the Oeological Survey were 

 based on the Chalk at the south-western end, which is now railed off 

 and has not been worked for some considerable time. The beds dip to 

 the south-west, thus allowing slightly higher Chalk to come in at that 

 end of the section, and this would account for some difference in the 

 horizons given. The present description is based on the vertical 

 section seen a few yards to the right of the railings which divide the 

 old from the new working. 



To the north-east of the pit the floor is formed by the Chalk Rock, 

 which is grass-covered ; consequently the soil has to be removed to 

 obtain an exposure. Several fossils representative of the Reussianum- 

 zone fauna were obtained from this bed, as well as the two fragments 



' " Geology of Loudon " : Mem. Geol. Surv., 18S9, vol. i, p. 76. 

 ; 2 " Cretaceous Rocks of Britaiu" : ibid., 1904, vol. iii, p. 217. 



^ " Excumon to Marlow" : Proc. Geo). Assoc, 1905, vol. xix, pp. lo7-8. 



