Notices of Memoirs — Prof. Lewis — Extra Morainic Lakes. 515 



others are those of the Cave-Hyasna. The three frota the dyke 

 represent the Cave-Bear, Rhinoceros tichorhinus, and a species of Deer. 

 Among the tunnel finds there were also three coprolites and a solitary 

 part of a left lower jaw of Hyaena divested of its lower boi-der — two 

 facts indicating that the Hyeena occasionally visited the tunnel. 

 Here also was found one, and but one, flint-flake tool. It has the 

 white colour so prevalent in the tools found in the cave-earth of 

 Kent's Hole, and was met with under circumstances admitting of no 

 doubt of its having been made and used by a human contemporary 

 of the Cave-Hygena in Devonshire. 



II. — On Some Important Extra-Morainio Lakes in Central 

 England, North America, and elsewhere, during the Period 

 of Maximum Glaciation, and on the Origin of Extra-Morainig 

 BouLDER-CLAY. By Professor H. Carvill Lewis, M.A., F.G.S.^ 



THE lakes so characteristic of all glaciated districts are due to 

 several causes. Some few are due to an actual glacial scooping 

 out of the rock floor, many to an irregular deposition of the drift, 

 by which former watercourses are obstructed, and still others to the 

 terminal moraine or to the glacier itself. These latter, known as 

 morainic lakes, may be divided into inter-morainic lalces, moraine meres, 

 and extra-morainic lalces, according to their position — back of, in, 

 or outside — the moraine. Extra-morainic lakes, if dammed up by 

 the ice front, are temporary in character, disappearing with the 

 retreat of the glacier ; but, as they may be of enormous extent if the 

 glacier is large, they may produce deposits of much geological 

 importance. Instances of such lakes occur in Switzerland, and 

 ancient examples 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 drainage 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 general absence of 

 strias or of glacial erosion or moraines in this district prove 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 has 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 

 Eocky Mountains, is 450 miles wide and over 1000 miles long. It 

 only occurs where rivers had flowed toioard 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, 



1 Abstract of a paper read at the Manchester Meeting of the British Association, 

 September, 1887. 



