EUROPE DURING THE GLACIAL PERIOD. 451 



In a paper before the British Association in September, 

 1887, Professor Lewis presented his views in greater detail, 

 and answered objections, alleging that — 



The hypothesis of extra-morainic fresh-water lakes, dammed 

 up by the glaciers, is sustained by all observed facts. The 

 most important of these lakes was one caused by the obstruc- 

 tion of the mouth of the Humber by the North Sea Glacier, 

 whose terminal moraine crosses that river at its mouth. This 

 large lake reached up to the 400-foot contour line, and ex- 

 tended southward nearly to London, and westward in finger- 

 like projections into the many valleys of the Pennine Chain. 

 It deposited the " great chalky bowlder-clay," and erratics 

 were floated in all directions by icebergs. It was bounded in 

 the vale of York by the Stainmoor Glacier, and Charnwood 

 Forest was an island in it. At its flood period it overflowed 

 southwestward by torrential streams into the Severn Valley 

 and elsewhere, carrying the "Northern Drift" into the south 

 of England. Other glaciers in England were bordered by simi- 

 lar but smaller lakes wherever they advanced against the drain- 

 age. Three such lakes were made by the Aire Glacier, the 

 largest of them extending to Bradford. The Irish Sea Glacier 

 caused many similar lakes high up on the west side of the 

 Pennine Chain, and at its southern end north of Wolverhamp- 

 ton. The overflow streams from the most southern of these 

 lakes joined those issuing from Lake Humber in the Birming- 

 ham district, characterized by a "commingling of the drift," 

 otherwise inexplicable. An examination of the supposed evi- 

 dences for glaciation. and for a great marine submergence in 

 central and southern England, shows that neither theory is 

 sustained by the facts. Thus, the supposed stria? on Rowley 

 Rag prove to be root-marks or plow-marks : those reported 

 at Charnwood Forest to be due to running water, or perhaps 

 icebergs ; the supposed drift on the chalk-wolds to be a local 

 wash of chalk-flints ; the high-level gravels on the Cotteswold 

 Hills to be preglacial ; the shells at Macclesfield, Moel Tryfan, 

 and Three Rock Mountain to be glacier-borne, and not a proof 

 of submergence ; the drift on the Pennine plateau of north 

 Derbyshire to be partly made by icebergs floating in Lake 



