182 W. J. MILLER PREGLACIAL COURSE OF UPPER HUDSON RIVER 



Warrensburg, while a short tributary^ having its source on the Stony 

 Creek divide, flowed northward to enter the Hudson. 



DRAINAGE OF LAKE GEORGE DEPRESSION AND EASTWARD 



The drainage history of this portion of the region has been ably pre- 

 sented by G. F. Wright, and also by J. F. Kemp, in the papers above 

 mentioned, and a very brief summary of that work is here given because 

 of its relation to the present discussion. The heavy drift accumulation 

 from Glens Falls northward has had much to do with the development of 

 the present drainage, especially as seen in the remarkable course of Half 

 Way Creek, which, though it has one of its sources in the city of Glens 

 Falls and close to the Hudson Eiver, flows northward into Lake Cham- 

 plain. Wright believes the pre-Glacial division of drainage between Lake 

 Champlain and the Hudson was near Fort Ann. He also believes that a 

 pre-Glacial divide existed at the narrows in Lake George, and that the 

 south-flowing stream from this divide went through Dunham Bay and 

 to the east of French Mountain. According to the present writer, this 

 stream, and also the south-flowing one from the Fort Ann divide, were 

 tributary to the pre-Glacial Hudson in the vicinity of Glens Falls. 



INFLUENCE OF ICE EROSION 



The elevation of the present Hudson Eiver west of Warrensburg is 

 about 620 feet, while its elevation when it passed through the pre-Glacial 

 channel southeast of the village was about 840 feet. This difference in 

 altitude of the channels must be accounted for either by inter-Glacial or 

 post-Glacial stream erosion or by ice erosion. While it is more than 

 likely that both of these processes have been effective, we shall now con- 

 sider only the influence of ice erosion. There is good evidence for vigor- 

 ous ice erosion of the Hudson Valley in the vicinity of Warrensburg, and 

 some of the facts favoring this view are as follows : ( 1 ) The great abun- 

 dance of scratched, polished, and rounded rock surfaces; (2) the com- 

 parative freshness of the rock, even in the case of the weak Grenville; 

 (3) the unusual softness and weakness of much of the pre-Cambrian 

 rock here due to the existence of extensive belts (forming valleys) of 

 thin-bedded, variable Grenville sediments; (4) the fact that these belts 

 of weak rocks must have been deeply decomposed during the long pre- 

 Glacial time, thus favoring extensive removal of material, and (5) the 

 north-south movement of the ice being parallel to these Grenville valleys, 

 and hence very favorable to ice erosion. 



We have in this region a good illustration of differential ice erosion, 

 because in the channel southeast of Warrensburg the unusual abundance 



