244 W. UPHAM — GLACIAL LAKES IX CANADA. 



raing of the waters of glacial melting and of rains on areas where the land 

 has a northward descent. While the ice-sheet was melting away from south 

 to north on such a slope, free drainage was prevented, and a lake was formed, 

 overflowing across the lowest point of what is now the southern "water-shed 

 of the basin. Many of these lakes were of small extent and short duration, 

 being soon, by the continued retreat of the ice, merged into larger glacial 

 lakes, or permitted to flow away where basins sloping northward are tribu- 

 tary to main river-courses draining southward. President Chamberlin has 

 well written of these lakes fringing the ice-sheet : 



" They vary in areal extent from trivial valleys blocked by ice to the broad expanses 

 of the great basins. If an attempt were made to enumerate all instances, great and 

 small, and all stages, earlier and later, the list of localities and deposits would swell, 

 not by scores and hundreds, but by thousands."* 



Evidences of Glacial Lakes. 



Five principal evidences of the former existence of glacial lakes are found, 

 namely, (1) their channels of outlet over the present water-sheds ; (2) clifls 

 eroded along some portions of the shores by the lake waves ; (3) beach 

 ridges of gravel and sand, often on the larger glacial lakes extending con- 

 tinuously through long distances ; (4) delta deposits, mostly gravel and sand, 

 formed by inflowing streams ; and (5) fine sediments spread widely over the 

 lacustrine area. A few words of general description may be given to each 

 of these before proceeding to note their special features for some of the more 

 important Canadian glacial lakes. 



Outlets. — Among the evidences of glacial lakes, the one most invariably 

 recognizable and most definite in its testimony is the outlet showing distinct 

 stream erosion across the rim dividing adjacent river basins, w4iich now in 

 many instances send their waters respectively to the Gulf of Mexico and to 

 Hudson's bay or the Gulf of St. Lawrence. Obviously, water-courses could 

 only exist in these positions as the outlets of lakes which were pent up by 

 some barrier that is now removed. Shore lines traceable northward from 

 these deserted channels must therefore belong to a lake, and cannot be re- 

 garded as the record of any marine submergence. 



Closely associated with such channels crossing water-sheds, and at the 

 same level, are the three following classes of proof cited, namely, eroded 

 cliffs, beach ridges, and deltas ; and below these shore records are the fine 

 lacustrine sediments. These are found in hydrographic basins which are 

 now drained by a continuous descent northward, presenting no indication 

 that any land barrier ever existed across their lower portions to form these 

 lakes, being afterward removed by erosion or by depression. The shore lines, 



* Proe. A. A. A. S., vol. XXXV, for 1886, p. 208. 



