WORK OF GLACIAL WATERS 147 



and volume. It will be very difficult to trace morainic belts across the 

 Hudson-Champlain Valley with certainty, though it is important to 

 know the lines of the receding ice-front. 



Work of glacial Waters 

 streams: erosion al 



Normal drainage. — It is apparent that the flow of glacial waters freely 

 away from the ice could occur only south of the divide, and as the pres- 

 ent divide was established by morainal filling and lies north of the pre- 

 glacial divide, much of the southward flow was drainage of ice-dammed 

 waters, and that some of the present south-leading channels were cut by 

 the glacial waters. The preglacial flow of the main streams was north- 

 ward, but the tributaries had various directions. The glacial drainage 

 took advantage of the favoring valleys and connected them into sequence 

 of southward flow. Tarr thought that the work of stream diversion and 

 of channel erosion was mainly pre-Wisconsin for the district described 

 in the Folio 169 (page 30). He specially cites the outlet of Cayuga 

 Lake, the gorge of Tioughnioga Creek, and the gorge of Chemung River 

 behind Hawes Hill, west of Elmira. The copious waters from the wan- 

 ing Laurentian ice-sheet were supplied with such volume of detritus that 

 they were largely aggrading agents. It is possible that the south-leading 

 valleys were mostly established by pre-Wisconsin glacial drainage, and 

 that the work of the latest glacial floods was chiefly transportative. In 

 the eastern half of the State the glacial outflow was freely into the Sus- 

 quehanna and Delaware escape or into the Hudson-Champlain marine 

 inlet, so there was no necessity for cutting new channels. 



The heaviest normal drainage was that in south-central New York, 

 concentrated in the Susquehanna, which cut the gorge south of Sayre, 

 Pennsylvania, and the river which drained Lake Iroquois through the 

 Mohawk Valley, the Iromohawk. This great river was the predecessor 

 of the St. Lawrence, which it probably exceeded in volume, as it carried 

 not only the outflow of the glacial Great Lakes, but the copious waters 

 from the glacial melting. 



Subglacial drainage. — This class of glacial si renins has been noted 

 chiefly in relation to eskers, which fall under another head in Ibis writ 

 ing. It is not likely that all eskers were laid down in the l>eds o[' streams 

 actually beneath or in tunnels under (he ice-sheet, though some probably 

 Were. Probably most subglacial or englacial streams were fully loaded 

 with detritus, and it' ( is not likely (hat many streams beneath the LC6 

 margin were so free of drift or under such hydraulic pressure as to seri- 



