520 S. V. WOOD, JTJN. ON THE NEWER 



lington and those other parts of the coast-section in Sheets 85 and 

 94 where its base rises above the beach, it is underlain by alternate 

 sheets of Purple Clay and of the blue Basement Clay, both containing 

 rolled chalk, but which in some places are separated by beds of dark 

 sand ; and just below these is the position (as it was described to 

 me) of the Dimlington bed of shells. In the vale of the Tees, and 

 in that of Central Yorkshire, it seems often to be made up of recon- 

 structed Lias shale and clay, finely laminated in places. 



The position which the Purple Clay thus occupies is not one which, 

 as a whole, is reconcilable with a marine deposit, though some of its 

 features, nevertheless, point in that direction. Being thus dissociated 

 from the Chalky Clay, but nevertheless overlying the Basement 

 Clay and the beds containing the Dimlington and Bridlington 

 Mollusca, we may regard it as either anterior to, synchronous with, 

 or posterior to the Chalky Clay. 



If anterior, it would belong to the later part of Stage II., and 

 thus to the period of greatest submergence, and be due to ice coming 

 from the north (for to ice coming in that direction this clay on the 

 east of the Wold is clearly due), after the ice of the Basement Clay 

 had retreated through the Humber. The absence of any marine 

 conditions in connexion with it above the level of, say 100 or 150 

 feet, however, and the absence of any gravel over it that could be 

 referred to this period, seem to render this supposition untenable — 

 the only gravel that overlies it along the Yorkshire coast-section, 

 except some mounds on the edge of the chalk-escarpment in the 

 south-east of Sheet 95 (and which appear to have been due to the 

 melting there of the Purple-Clay ice, as the cannon-shot gravels were 

 to that of the Chalky-Clay ice in West Norfolk) being the Hessle, 

 and gravel even later than that, and these gravels are confined to 

 levels below 100 feet. 



If synchronous with the Chalky Clay, the part west of the Wold 

 should be continuous with that clay, though, the part lying east of 

 the Wold being due to an independent arm of ice, the absence of 

 this continuity has not the same significance. There seems, however, 

 to be a hiatus between this western part and the Chalky Clay, which 

 dwindles away northwards by a chain of small patches decreasing in 

 that direction, while nothing like a transitional character is assumed 

 by the clays as they approach each other. Moreover, while the 

 Chalky Clay all over that part of its range which is nearest to the 

 Purple rests on the Mesozoic formations directly, and in places has 

 the gravel e over it up to the level which I have described as falling 

 towards the Wash, the Purple Clay appears to pass over that gravel 

 in the railway-cuttings between Eetford and Bawtry, in Sheet 82. 



I therefore think that, though the eastern arm of the Purple 

 Clay, which is that in which the Shap blocks abound, may be, and 

 probably is, though unconnected with it, at least partially coeval 

 with as well as later than the Chalky Clay, the western arm is 

 posterior to it, and represents moraine which, after the ice of the 

 latter had disappeared and allowed the sea to enter the area of the 

 Lower-Trent drainage-system up to the level to which the progress 



