DUIl rs OF KLAMIJOKOLUll iii:\u. 425 



ill places nearly stationary, and thaw p^raduully away, leaving its 

 solid contents in the form of the Upi)er Clay. 



(5. The Seiverhji Gravels and Newer Beih. — These beds need little 

 further discussion. As already suggested, the " Bridlington Series '' 

 (ISewerby Gravels and Hilderthorpo Sands) seeras to replace the 

 Upper Clay, and to have been deposited at about the same period as 

 that clay by strong currents of fresh water issuing from the Main 

 Wold Valley, perhaps dammed back by the ice which may still 

 have covered the eastern part of Holderness *. 



On the outskirts of Bridlington Quay are newer gravels (the 

 " Gypsey Gravels ") evidently deposited at a still later period by a 

 reduced though yet considerable volume of water from the same 

 valley, when the stream had no direct route to the sea and turned 

 southwards to seek the Humber (see p. 388). 



Similar gravels are found at the mouths of most of the Wold 

 valleys opening upon Holderness, as at Lowthorpe, Driffield, &c.t, 

 and indicate a climate very different from that of to-day. I have 

 suggested % that they were formed when the winters were so severe 

 that the upper layers of the Chalk were choked with water and per- 

 manently frozen, thus rendering the rock impervious so that it shed 

 off the water torrentially § during the summer thaw. It was at 

 this period that the excavation of the now dry Wold valleys was 

 completed. At Bridlington these gravels are occasionally inter- 

 bedded with peaty silt and freshwater marl, and are proof that the 

 area has not suffered marine submergence since the Glacial period. 



YII. Notes on the Correlation of the Drifts. 



That this investigation should have led to the adoption of a tri- 

 partite division, as the most natural and the most convenient, not 

 only for the drifts of Flamborough Head, but also of Holderness, is 

 really, in the main, no more than a confirmation of the work of the 

 earlier observers. John Phillips || seems from the first to have been 

 of this opinion ; so also, for the drifts north of Flamborough, Martin 

 Simpson ^, and the officers of the Geological Survey of the coast 

 between Scarborough and the Tees **. The difficulties which after- 

 wards arose were chiefly owing to the theory of W'ood and Rome, 

 that the " Basement Clay " was confined to Southern Holderness 



* See ' Glacial Sections,' part iii. supra cit., for full details of these later 

 beds. 



t Geol. Survey Mem. ' DrifReld,' p. 15. 



+ Proc. Yorks. Geol. & Polytecbn. Soc. vol. viii. (1883) p. 249. 



§ It has since been shown by Rev. E. M. Cole, F.G.S., that this effect is still 

 occasionally produced on the Wolds when a sudden thaw follows a very severe 

 I'rost ; see ' Note ou Dry Valleys in the Chalk,' Proc. Yorks. Geol. & Poly- 

 tecbn. Soc. vol. ix. (1887) p. 343. 



II ' Geology of Yorkshire,' 3rd ed. pt. i. p. 163. 



•; Geol. & Nat. Hist. Repert. (1865) vol. i. p. 57. 



** Geol. Survey Mems. ' North Cleveland,' by G. Barrow, p. 65 ; ' Whitby 

 and Scarborough,' by C. Fox-Strangways and G. Barrow, p. 52 ; ' Eskdalo,' 

 by C. Fox-Strangways, G. Barrow, and C. Reid, p. 51 ; also ' Northallerton 

 and Tbirsk,' by 0. Fox-Strangways, A. G. Cameron, and G. Barrow, p. 54. 



U. J. G. S. No. 187. 2 G 



