424 MR. G. W. LAMPLUGH ON THE 



the residuum left behind on the melting of a sheet of ice charged 

 with clay and stones. This theory certainly accounts for many 

 features in it which are otherwise difficult of explanation, such 

 as its uniform texture, its relation to the stratified deposits along 

 drainage-channels, its extension beyond the limits of the rest of 

 the drift, and its behaviour on the Chalk slopes and on the flanks 

 of the gravel-mounds. But setting aside this debatable question as 

 being too wide for full discussion in this paper, while accepting for 

 the clay, as most have done who have studied it *, an origin in 

 some way or other the result of land-ice, its composition and distri- 

 bution seem necessarily to postulate the continued blockade of the 

 Korth-Sea basin by an ice-sheet during its formation. The 

 abundant fragments of Carboniferous and other jN^orth-Country 

 rocks contained in it at Flamborough, together with the absence of 

 the clay from the higher and from the westward part of the 

 AVolds, show that the Teesdale ice has still come coastwise, and 

 not across the Wolds ; and for that ice to have taken such a 

 course necessarily implies the presence of some great obstacle barring 

 its passage eastward in the North-Sea basin. This ice, in coming 

 down the coast north of Tlamborough, seems to have been shoul- 

 dered in, as it were, upou the land, and sometimes forced up into 

 the open valleys of the Yorkshire coast. Hence the predominance 

 of Carboniferous rocks in the drifts of the headland and the country 

 to the north of it, as shown in the Boulder lists. 



This could scarcely have taken place had not the North-Sea 

 glacier still held its ground ; and it would appear, therefore, 

 that the retrocession indicated by the stratified series went no 

 further than, at the most, to carry the margin of the ice back a 

 few miles from our coast, the character of the junction between 

 the Intermediate beds and the Upper Clay being frequently 

 such as to show gradually changing and alternating conditions 

 without any considerable interval of interruption. And that the 

 Upper Clay should extend beyond the limits of the older drift seems 

 to indicate that in the later stages of the Glacial period, while the 

 North-Sea glacier was gradually diminishing, there was a great 

 augmentation in the quantity of ice flowing from the Pennine 

 chain t, which was pent in upon the east coast and overstepped the 

 old moraines. At a later stage the continued decadence of the 

 North-Sea ice may at length have opened a path due eastwards for 

 the Teesdale and other North-British glaciers, whereupon the coast- 

 wise current, being tapped at the source, would suddenly cease ; and 

 the East Yorkshire branch, receiving no fresh supply, would become 



* S. V. Wood's later papers ; Mr. Clement Eeid's ' Holderness ' Memoir, 

 p. 42 ; Prof. Jas. Geikie's ' Great Ice Age,' 2ncl ed. p. 374. 



t The wide obliteration of the open-water surface surrounding Scandinavia 

 and the northern portion of our own islands through tlie eucroacluuent of the 

 ice-sheet would probably shift westwards the area of greatest precipitation, and, 

 as the ice-flow must always be dependent on the snowfall, this may have brought 

 about the conditions noted above. (See abstract of ' East Yorkshire during the 

 Glacial Period,' in Kep. Brit. Assoc. 1890). 



