172 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



of the upper end of the ti'ough containing it. Such a glacier, 

 melting beneath the sea after the submergence had taken place 

 which gave rise to the purple clay and sj)read it over the higher 

 "VTolds, would leave a void in the part where it had existed and 

 kept out the sea duiing the chalky clay deposit, and this void 

 would then become filled with the pui^le clay. This alternative, 

 which acquires some countenance from the remarkable rise in the 

 floor of the great depression immediately south-west of Malton, 

 seems to us far the more probable of the two suggested*. 



The position of the pui-ple clay on the summit of the lofty Wold 

 at Speeton, as well as the absence of any kind of chalky debiis in 

 aU but the lower portion of the same clay in Holderness, seems to 

 us to point to the conclusion that the submergence giving rise to it 

 involved Lincolnshire and the more southern parts of England as 

 well as the Yorkshire "\^old. As these parts, however, were more 

 remote from the probable source of the purple-clay sediment (which 

 was the Older Secondary and Carboniferous region of Northern 

 Yorkshire, and of the "VTestmoreland and Cumberland Pells), this por- 

 tion of the Upper Glacial clay may have attenuated southward ; 

 but, however this may be, it has aU been removed in that part by 

 the marine Postglacial denudation, the increased operation of which 

 southwardly and west war dly, and its great prolongation over the 

 south and south-west of England, it was the endeavour of the first- 

 named of us to show in the paper before referred to in the last volume 

 of this Journal. 



The denudation of the purple clay is, from its present position 

 (stretching northward in a continuous belt along the coast, but 

 wholly removed for a great distance westward, i. e. inland), shown 

 to have proceeded in the opposite direction to that in wliich the 

 Xorth Sea occurs, the entire Wold-suiface of Yorkshire and Xorth 

 Lincolnshire being, with this exception ( and that of an outlier, about 

 a furlong square, which still remains at Huggate, near the opposite or 

 western extremity of the "Wold, at an elevation of about 600 feet) , 

 destitute of it, as well as the low country at the TTold-foot from 

 Muston westwards. An outher of what seems to be the same clay 

 first meets us westwards fi^om this coast-belt, at a distance of about 

 25 miles, namely, in the deep railway-cutting at Gate Helmsley, 

 6 miles E.X.E. of York'(whence the same clay occupies much of the 

 ground northwards by Plaxton and Earton Hill), and thus attests 



* In the x^aper of Mr. Judd upon the Speeton clay, read before the Society 

 subsequently to this of ours, the section of FUey Bay was shown as including 

 a Praeglacial forest-bed beneath the Grlacial clay. The presence of such a bed 

 would, if it existed, seem fatal to the second of the above explanations, since 

 the grindhag of such a glacier as we have supposed would have quite destroyed 

 so feeble a deposit as a forest-bed. The last-named of us, however, in a reex- 

 amination of the coast, since Mr. Judd's paper, and during a favourable exposure, 

 after stonns, of the chif-base, not only failed to detect any such bed, but dis- 

 closed a hgnite (of Kimmeridgian age) containing the impressions of Ammonites, 

 occupying for a considerable distance the part indicated, and overlain directly 

 by the purple clay, the resemblance, as far as the eye is concerned, to the 

 forest-bed of the Korfolk coast beneath the G-lacial clay being sufficiently 

 striking. 



