DKIFTS OF FLIMBOROUGII HEAD. 393 



east of Potter Hill, and mounts by a long slope to the top of the 

 Chalk as shown iu fig. 4. 



The laminated clay (4 a, fig. 3) becomes associated with chalky 

 gravel and sand, and seems finally to pass into stony Boulder-clay and 

 to be absorbed into the Basement Clay, except its uppermost layers, 

 which are prolonged as a thin seam of silty gravel (3 h) between 

 the two Boulder-clays overlying the Chalk (PI. XIII. fig. 4). 



The behaviour of the Purple Clay is unexpected, and deserves 

 especial attention as elucidating many perplexing difierences between 

 the low-level and high-level drifts. South of Potter Hill * there 

 are two well-marked bands of Purple Clay, separated by chalky 

 gravel from 2 to 6 feet thick ; but when these reach the rising 

 ground the lower band is shredded out among stratified loam, silt 

 and sand, and disappears altogether, while the upper division is also 

 partly absorbed among similar, though rather more gravelly, beds. 

 The remaining portion of the upper division passes over the dome- 

 shaped mass of stratified beds, which thus almost monopolize the 

 section (PI. XIII. fig. 3). 



This hill is evidently a mound of the same character as those of 

 the kame-like chain already described, but its true outline is partly 

 masked by the Sewerby Gravels. 



Xorth of the hill the stratified beds seem, amid great confusion, 

 to pass back into Boulder-clay, but this part of the section is still 

 overgrown and obscure. Beyond this point, however, the Boulder- 

 clay overlying the Basement Clay is in one mass (PI. XIII. fig. 4) 

 without divisions. 



(c) Sewerhy. — The two Boulder-clays above the Chalk at Sewerby 

 represent, therefore, the lower, the Basement Clay of Holderness, 

 and the upper, whatever remains of all the overlying divisions, 

 though, as will presently appear, the correlation holds good only in 

 a broad sense. 



The Sewerby Gravels (2 h) in this part of the cliff, and indeed 

 generally, contain a large proportion of flattish subangular fragments ' 

 of chalk, usually measuring up to 2 or 3 inches in breadth, but in 

 a few places ranging up to 8 or 10 inches. These " platy " fragments 

 are such as might result from the shivering by frost of the hard 

 Yorkshire Chalk, with a subsequent slight washing of the detritus. 

 Taken in connexion with the presence elsewhere of similar chalky 

 gravels (as at Danes' Dj^ke) at other horizons in the drift, and the 

 scarcity of chalk in the Boulder-clays of the headland, they seem 

 to indicate an exposed Chalk surface in the neighbourhood through- 

 out Glacial times t. 



In the cliff" south of Sewerby, for the first time in the coast- 

 sections, the base of the Glacial beds is brought above high-water 

 mark. Here the Basement Clay is seen to rest upon a thick bed of 

 compact chalky rubble (5, of fig. 4), the junction between them 



* For this section, see J. E-. Dakyns, ' Glacial Beds at Bridlington,' Proc. 

 Yorks. Geol. & Polyteehn. Soe.vol. vii. (1870) p. 123; ormy paper on 'Glacial 

 Sections,' part i. supra cit. 



t ' Glacial Sections,' part ii. supra cit. p. 36. 



Q.J.G.S. No. 187. 2e 



