MOHAWK GLACIAL LOBE 725 



Valley. The fact of standiner water over Northville has been recognized by 

 Professor Brigham, and the lake is mapped and described by myself in an 

 unpublished bulletin of the New York State Museum. 



MOHAWK GLACIAL LOBE 

 BY ALBERT PERRY BRIGHAM 



(Abstract) 



The limits of the Mohawk glacier; relation to glaciers of the Adirondacks, 

 Catskills, Hudson Valley, and central New York ; character and extent of topo- 

 graphic changes due to ice-work ; mode of retirement of the ice ; water-laid 

 formations and glacial lakes ; drainage modifications of the Hudson and Sacan- 

 daga rivers. 



Discussion 



Professor Brigham replied as follows to a question by Professor Fairchild: 

 Two critical localities were observed with care. A few miles north of the 

 head of Otsego Lake there is no sign of cutting at the watershed, which is 

 between Si)ringfield Center and Vanhornesville. In fact, low hills with mo- 

 rain ic jontours, unmarred by later changes, pass completely across the valley 

 at the point of divide. There is no cutting on the Delanson col, which is 

 floored with till, bearing many angular and unwashed fragments of the drift. 

 There are no marks of wave action on the slopes westward to Esperance 

 Station. There are no indications of a large outlet stream at Duane Station 

 or down the gorge of the Boxen Kill. This gorge in its lower part is strongly 

 developed, but it is excavated in shales and is nicely adjusted to the vigorous 

 stream which is now at work. Its tributary gorges also, which could have 

 carried no Mohawk waters, are comparable to the main gorge in their devel- 

 opment. Farther up the Boxen Kill, frail morainic hills still extend down to 

 the stream in a position in which a greatly enlarged current must have 

 eroded their streamward slopes. 



Prof. Lawrence Martin : Are there recessional moraines laid down in the 

 waters of marginal glacial lakes? Are they weaker than the other moraines? 



Professor Brigham replied : No water-laid or other moraines were seen 

 which would correlate with waters having an outflow across the Delanson col. 

 In fact, the central and southern parts of the Amsterdam and Fonda quad- 

 rangles are exceptionally free from morainic accumulations. 



In a paper presented hastily at the Baltimore meeting and not yet pub- 

 lished, I showed how the Adirondacks at one stage in the waning of the ice- 

 sheet had become partially uncovered and stood as an island, so to speak, in 

 the sea of ice. The waters from the melting of the inclosing ice produced 

 high-level lakes in the Adirondack valleys, which accounts for the elevated 

 and extensive sand-plains encountered in the Adirondacks. These waters of 

 the Adirondack stage had no escape except southward across the strait of ice 

 in the Mohawk Valley to Susquehanna drainage. Some peculiar features of 

 ancient stream-work at the head of the Otsego Valley are attributed to this 

 overflow. During the Adirondack stage of the glacial waters an extension of 

 the Hudson ice lobe pushed westward up the Mohawk Valley, as indicated by 

 the striae on Professor Brigham's map, and produced a group of excellent 



