WOOD AND HOME LINCOLNSHIKE AND S.E. YORKSHIRE. 151 



the coast-section we see the Hessle gravel confined to the lower 

 part of the troughs of denudation cut through or into the purple 

 clay, and the Hessle clay (e) alone spreading over and enveloping 

 the more considerable hills formed of purple clay, such as that of 

 Dimlington ; but occasionally the gravel (d) occurs far up the de- 

 nuded slopes of the subjacent purple clay. The Hessle clay has a 

 general uniform thickness varying from 10 to about 20 feet, and 

 may be said to wrap the whole of Holderness and East Lincolnshire 

 like a cloth, spreading over and enveloping the denuded edges of the 

 basement and purple clays, and beyond them extending some way 

 over the chalk itself, reaching up the eastern slope of the Wolds to 

 elevations approaching 150, and perhaps even 200 feet, but not 

 now maintaining any constant elevation. Beyond that altitude, 

 however, we have failed to detect it. The wrapping nature of 

 this clay, enveloping hill and valley alike up to elevations between 

 100 and 200 feet, and the posteriority of it to the formation of the 

 valley-system by denudation in the interval that followed the 

 elevation of the Glacial beds, may be seen by figs. 1, 5, and 11, 

 the two latter showing its overlap beyond the purple clay. The 

 valley (or Postglacial) structure thus attaching to the Hessle Boulder- 

 clay is of great importance in showing its total disconnexion with 

 the great Glacial clay-formation with which it has hitherto been 

 confounded ; for although the purple clay may, in the sense that it 

 occupies the valley beneath the northern "Wold-foot, and also fills 

 ancient valleys north of Plamborough, be called a valley-deposit, 

 yet it was deposited during a submergence that not only involved 

 those valleys but also the lofty Wold-summits, and even much 

 greater altitudes * ; whereas the Hessle clay is the deposit of a 

 very partial submergence, not exceeding apparently from 150 to 200 

 feet, and was accumulated after the valleys had been formed by 

 the earlier Postglacial denudation out of the Upper Glacial clay. 

 Along the coast we lose this clay a little north of Bridlington, where 

 the chalk and purple clay begin to occupy altitudes exceeding 

 100 feet. Notwithstanding this true Postglacial age of the deposit, 

 the Hessle clay is really a genuine Boulder-clay ; and although its 

 boulders are generally of no great size, some of considerable dimen- 

 sions occur in it. One of these, containing several cubic feet, and 

 covered with glacial striae, was brought from the Hessle section, 

 and is now in the Museum of the Literary and Philosophical Society 

 at HuUt. The colour of the Hessle clay, coupled with the presence 

 of the chalk-fragments and the boulders in question, seems to show 

 that it has been mainly formed, and its boulders derived, from the 



Phillips, it nevertheless seems to us that if he concedes, as he seems disposed to 

 do, the separate and newer age of the Hessle cla^ from the mass of the clay in 

 section on the Holderness coast, any objection to the age we assign to the gravel 

 becomes removed. 



* We infer this great submergence not merely from the absence of chalk, but 

 from the abundance of boulders of Shap granite in the purple clay from Flam- 

 borough to the Tees. 



t This, we infer, was derived at second hand from the purple, or else from 

 the basement, clay. 



