DRIFTS OF FLAMBOl:Oron IlKAD. 423 



sea, the result of tliese conditions is still more marked. From this 

 cause may arise the rapid increase in the ])roportion of gravel to 

 clay as the drifts api)roac]i tlie hilly ground *. 



if the relation of the Purple Clay to the Intermediate beds be 

 such as I have described, it is evident that the replacement of the 

 one by the other Avill rarely be suddenly marked, but will take 

 ])luce gradually, as the beds are traced across the space once 

 occu])ied by the ice-margin. 80 also the limits of the Lower and 

 of the Upper lioulder-elays will be only more or less vaguely 

 deli n able. 



The cause and the extent of the recession indicated by the strati- 

 fied beds will be more conveniently considered in the next section, 

 wherein the Upper lioulder-clay is treated of. 



5. The Upper Boulder-elai/. — The distinguishing features of the 

 Upper Clay of Flamborough Head are that it is redder in colour, 

 more earthy and less compact in texture, and less irregular in thick- 

 ness than the lower division, and hns fewer boulders. As already 

 mentioned, it evidently comprehends the top clay of Holderness (the 

 '• Hessle Clay " of AVood and liome), that deposit being by no 

 means the " low-level " or valley deposit which those authors sup- 

 posed t. Its limits on Plamboroagh Head and elsewhere need not, 

 however, be strictly the same as those of the Holderness bed. It 

 is- decidedly thicker at low elevations, but is persistent over the high 

 ground on the north face of the headland, where the Basemejit Clay 

 apparently sometimes dies out (PI. XIII. fig. 11). Its westward 

 limit on the AVolds cannot be clearly traced, but seems to depend 

 more on the proximity of the range of gravel-mounds than on either 

 the shape or elevation of the surface. Though the identification is 

 ])erhaps not quite convincing, it seems to be this clay which covers 

 thiidy and interruptedly the inner edge of the "Wolds, beyond the 

 limits of the gravels, up to elevations of 250 feet + almost every- 

 where between Plamborough and the Humber. Even at low ele- 

 vations it seems sometimes to be replaced by stratified beds, as on 

 both sides of Bridlington Quay, and in a few sections in Holderness ; 

 and it frequently shows a tendency to pass into the underlying 

 gravels. In many respects it bears a close analogy to the '• Fringe " 

 or '•'Extra-Morainic Boulder Clay " of America, whose origin has 

 given rise to so much discussion among Transatlantic glacialists. 

 I do not see how it can have been formed except by land-ice, but 

 it hardly bears the characters one would expect in a basal moraine, 

 and I am tempted to apply to it the theory of the origin of Boulder- 

 elavs so ably advocated by Mr. J. G. Goodchild § in England, and 

 Prof. A. H. Winchell and others in America {;, and to regard it as 



* See S. Y. Wood. Quart. Journ. Geol. Soc. vol. xxxvi. (1580) p. 503. 



t Quart. Journ. Geol. Soc. vol. xxiv. (18l38) p. 151. 



t Geol. Survey Mem. 'Driffield,' p. 13. 



§ Quart. Journ. Geol. Soc. vol. xxxi. (1875) p. 99 ; Geol. Ma?. (1874) 

 p. 49(i ; Trans. Cumberl. &, Westmorl. Assoc. Lit. &. Sci. vol. xii. (1S87) pp. Ill 

 et segq. 



II Jas. Geikie, ' Great Ice Age,' 2ud ed. p. 460. 



