516 Notices of Memoirs — Prof. Lewis — Extra Morainic Lakes. 



and have been the subject of much discussion ; being held by some 

 to be proof of marine submergence, by others to be the ground- 

 moraine of a glacier. The " great chalky boulder-clay " is the best 

 known of these deposits. There are serious objections to the two 

 theories heretofore advanced to explain this, whilst the hypothesis of 

 extra-morainic freshwater lakes, dammed up by the glaciers, is 

 sustained by all observed facts. The most important of these lakes 

 was one caused by the obstruction of the mouth of the Humber by 

 the North Sea glacier, whose tei'minal moraine crosses that river at 

 its mouth. This large lake reached up to the 400 feet contour line, 

 and extended southward nearly to London, and westward in finger- 

 like projections into the many valleys of the Pennine Chain. It 

 deposited the " great chalky boulder-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 south-westward 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 similar but smaller lakes wherever they advanced against the 

 drainage. 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 Wolverhampton. The overflow streams 

 from the most southern of these lakes joined those issuing from Lake 

 Humber in the Birmingham district, characterized by a " com- 

 mingling of the drift," otherwise inexplicable. An examination of the 

 supposed evidences 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 striae on Eowley Eag 

 prove to be rootmarks or ploughmarks ; 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 pre-glacial ; the shells 

 at Macclesfield, Moel Tryfaen, and Three Eock 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 Humber, and partly a decomposed Millstone Grit 

 or Bunter Sandstone ; and the Welsh erratics on Frankley Hill at a 

 height of 800 feet to be due to a more ancient glaciation. 



The conclusion that the glacial phenomena of England are due 

 neither to a universal ice-cap nor to a marine submergence, but to a 

 number of glaciers bordered by temporary fresh- water lakes, is in 

 accordance with all the observations of the author in England and 

 elsewhere. 



Postscript. — Since the paper was read, of which the above is an 

 abstract, 1 have found traces of the existence of a very much older 

 series of glaciers than those here described. Since the period of 

 these ancient glaciers, which in many places were more extensive 

 than the modern ones, earth movements have occurred and erosion 

 has removed almost all their deposits and generally obliterated the 



