ANCIENT WATER LEVELS OF CH.\ M PL A IN— HUDSON VALLEYS 75 



base leveling in which the ancieni floor of the Hudson valley was 

 worked out. 



Davis 1 in 1891 referred the excavation of the Hudson valley to 

 Tertiary time and the cutting of the trench in this lowland to late 

 Tertiary or a post-Tertiary beginning. 



Rock channels of the upper Hudson valley. The Hudson gorge 

 is fairly well defined as far north as Fort Edward by the present 

 course of the river. At that point the river falls into this rock 

 channel from the west very much as the Mohawk falls into it at 

 Cohoes, but the rock gorge is traceable north-northeast into the 

 Lake Champlain valley. 



The divide today between the Hudson drainage and the Cham- 

 plain drainage in this gorge lies about 5 miles northeast of Fort 

 Edward and is a scarcely perceptible watershed 147 feet above 

 sea level. It is owing to this feature that the Champlain canal 

 connects the two drainage basins with relative ease and few locks. 

 [See the Glens Falls quadrangle for details of the topography] 



The present course of the Hudson from the eastern edge of the 

 Adirondacks to Fort Edward is evidently of postglacial origin, 

 for the river runs over ledges at Fort Edward, at Bakers Falls, 

 at Sandy Hill and again at Glens Falls, dropping from the 300 

 foot contour at the edge of the mountains to about 130 feet at 

 Fort Edward. West of Glens Falls the river has sunk its bed 

 in meanders into the glacial sands which form a delta made on 

 the melting out of the ice which lay in the lowlands in this upper 

 part of its valley. These sands thickly cover the bed rock topo- 

 graphy. Whether the river in preglacial times flowed southward 

 so as to join the Hudson gorge at or below Fort Edward or turn- 

 ing to the north just west of Glens Falls and following the valley 

 of Halfway creek emptied into Lake Champlain is at present an 

 open question, which can only be decided on evidence from bor- 

 ings which are at present wanting in this section. 



It is evident that Halfway creek flows in a well defined channel 

 but partly filled by the debris of the last ice invasion [see Glens 

 Falls sheet]. 



Ballston channel. From near Schenectady an old rock channel 

 trends north-northeastward by Ballston toward Saratoga. South 



'Bost. Soc. Nat. Hist. Proc. 1891. 25 :318-35. 



