TRANSACTIONS OF SECTION C. 693 



morainic lakes, accordinn- to their position — back of, in, or outside — of the moraine. 

 Extra-morainic lakes, if dammed up by the ice front, are temporary in character, 

 disappearin;; with the retreat of the glacier; but, as they may be of enormous 

 extent if the i^lacler is larg-e, they may produce deposits of much geological 

 importance. Instances of such lakes occur in Switzerland, and ancient exarnples 

 occur as well in Northern Germany, Asia, North America, and Central England. 

 They are to be expected wherever a glacier advances against or across the drainao-e 

 of a country. Mr. Belt supposed that Northern Asia was covered by a lake of this 

 character, caused by the Polar glacier obstructing the rivers flowing north. 



In North America, where the terminal moraine has been accurately mapped for 

 thousands of miles, deposits of boulder-clay and erratics occur outside of the 

 moraine, and have been supposed to be due to an older glacier in the first glacial 

 epoch. But the entire absence of strife or of glacial erosion or moraines in this 

 district proves that a glacier was not the agent of deposition. Nor are there any 

 traces of marine life in the deposits. This extra-morainic boulder-clay is narrow- 

 in Pennsylvania, where the 'author had called it 'the Fringe,' but west of the 

 Missouri is 70 miles wide ; and in British America, between the great moraine 

 called the ' Missouri Coteau ' and the Rocky Mountains, is 450 miles wide and over 

 1,000 miles long. It only occurs where rivers had flowed toward the glacier, and 

 is explained as the deposit of great temporary freshwater lakes dammed up by the 

 ice-front, the erratics having been dropped by icebergs. 



Similar deposits occur in England outside of the terminal moraine, and have 

 been the subject of much discussion ; being held by some to be a 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 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 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-clav,' 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 Brad- 

 ford. 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 over- 

 flow ?trea_ms from the most southern of these lakes joined tho.=e issuing from Lake 

 Humber in the Birmingham district, characterised by a ' comminghng 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 stria3 on 

 Eowley Rag prove to be rootmarks or ploiighmarks ; those reported at Charnwood 

 Forest to be due to running water or perhaps icebergs ; the supposed drift on the 

 chalk wolds to bo a local wash of chalk flints ; the high-level gravels on the 

 Cotteswold Hills to be pre-glacial ; the shells at Macclesfield, Moel Tryfan, and 

 Three Ptock 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 supposed Welsh erratics on Frankley Hill at a height of 800 

 feet to be in place and due to an outcrop of the paleozoic floor. 



The conclusion that the glacial phenomena of England are due neither to a 

 universal icecap 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. 



