discussion of clutrria for discrimination 193 



Discriminative Criteria 

 glacial waters 



The study and explanation of puzzling or equivocal features, like high- 

 level sand-plains, appears to have been evaded by referring them to the 

 limbo "glacial/^ The term is overworked. It is unscientific to attribute 

 such [)lains and unexpected shore features to glacial waters without proof, 

 and it is unfair when other explanation has been given. It seems neces- 

 sary to discuss the criteria for discrimination of the glacial plains. 



In valleys declining northward, or in any direction toward the waning 

 ice-sheet, ice-impounded or glacial waters were certainly held. This may 

 also be true of some valleys with only a part of their course so oriented 

 as to permit temporary blockade. The Androscoggin Valley is a possi- 

 ble example. In all such valleys high-level deltas and shore features 

 are regarded with suspicion and are not used as evidence of sealevel 

 waters, at least not without careful discrimination. ]\Iany such examples 

 of ice-damned valleys are found on the north-facing slopes of the basins 

 of the Great Lakes and on the south wall of the Saint Lawrence Valley in 

 New York, A'^ermont, and Quebec. Many of the glacial lakes in New 

 York have been the subject of published papers. 



Glacial lakes were practically impossible in the great south-leading 

 valleys like the Hudson and Connecticut, the reasons being given in a 

 former paper (84, pages 291-292). The same is true of all valleys which 

 were normal to the glacier front and opened freely seaward, like those 

 of Maine and New Brunswick. 



The glacial waters, which were temporarily held in embayments of the 

 walls of large valleys, like the Hudson, Penobscot, or Saint John, did not 

 commonly produce any important features or any difficult of diagnosis. 

 Deltas and short features in the lateral valleys are the only ones of doubt- 

 ful origin, and of these some discussion is desirable. 



The damming of waters, with effieieut length of life in the tributaries 

 of the south-leading trunk valleys, required decided lobation of the ice- 

 margin, probably to an amount not common, and something more than 

 a low tongue of the thin edge of the ice-front. But such pondings in 

 the lateral valleys did sometimes occur. High-level phenomena above 

 the well-determined marine level are so ex]^laiued. 



To have a long life and stoacly level, so as to produce good shore 

 features, glacial lakes, like auy other class of lakes, rcquii'ed fixed out- 

 lets. That means outlet over land, and such outlet should be located, if 

 a long-lived, constaut-level glacial lake is postulated under doubtful con- 

 ditions. Most glacial waters had their outflow along the margin of the 



