32 NEW YORK STATE MUSEUM 



Mohawk rivers. A very long time intervened between the 

 extinction of Lake Amsterdam, estabhshing free drainage through 

 the Mohawk valley, and the beginning of the present river. That 

 interval was the glacial flow that endured until the Laurentian ice 

 body weakened north of the Adirondacks sufficiently" ' to open an 

 escape for Lake Iroquois on the international boundary,^ across 

 Covey hill, lower than the Rome outlet. 



Two periods of the glacial flow have been discriminated by the 

 writer; one called the Glaciomohawk, which covered the flow 

 previous to the establishing of Lake Iroquois, and the Iromohawk, 

 the outflow of the Iroquois waters (see title 17, p. 38). The 

 Glaciomohawk river endured while the central- New York waters 

 passed through four stages : the later Lake Vanuxem, the free 

 drainage succeeding Vanuxem, the restored Vanuxem and Lake 

 Warren (see State Mus. Bui. 127, plates 37-40). It is possible 

 that the readvance of the ice front in the Syracuse district, during 

 Second Vanuxem and Warren time, was accompanied by con- 

 temporary advance of the Hudsonian lobe so as again to block the 

 Mohawk and produce a second Lake Amsterdam, but it is now only 

 conjecture. 



The Iromohawk endured from the time when the ice left the Rome 

 district to the time when it had abandoned the Ontario basin and 

 lay against Covey hill, on the north boundary of the State. 



The volume of the Glaciomohawk was always much greater than 

 that of the present river, and for part of its life it received all the 

 drainage of central New York from as far west as LeRoy. The 

 Iromohawk was a larger river than the St Lawrence. It not only 

 carried the precipitation of the St Lawrence basin but received in 

 addition the contribution from the melting of the accumulated ice 

 body. 



Remnants of the Iromohawk flood plains in the form of low 

 terraces occur along the valley, especially near the junction of 

 larger tributaries. They range in altitude from 440 feet at Utica 

 to about 380 at Amsterdam and 360 at Schenectady. 



The relation of Lake Albany to the glacial Mohawk is not clear. 

 With the recession of the ice front from Schenectady we lose the 

 key to correlation which we possessed during the earlier history, in 

 the relation of ice-border channels to lake planes. The capacity of 

 the intrenched channel of the river below Schenectady seems insuf- 



1 Science, XXVI, 399; Sept. 27, 1907. Also (title 40) N. Y. State Mus. 

 Bui. 84, p. 161-64, pi. 25. 



