r38 NEW YORK STATE MUSEUM 



session of the pass at Kome, *and the vast Iromohawk river pro- 

 ceeded to grade the valley. 



The later level of the Iromohawk planing is represented by 

 numerous remnants of its flood plains. So far as observed, these 

 are about 20 feet over the present Mohawk flood plain. A good 

 fragment of the Iromohawk plain may be seen on the west side 

 of Ninemile creek, 2 miles north of Oriskany village; also along 

 the north side of the valley between Frankfort and Utica. 

 Doubtless these remnants of the Iromohawk plain may be identi- 

 fied in numerous localities. The difference in altitude between 

 the Iromohawk and the Mohawk plains, only about 20 feet, 

 agrees well with the apparent amount of down cutting by the 

 present river at the head of the rapids in Little Falls [see p. r33] . 



Summary. There are three stages which we can clearly 

 recognize in the history of the valley drainage since the valley 

 was buried under the ice sheet. 



1 The Pre-Iroquois or Glaciomohawk waters. These were 

 held in the valley during the ice retreat. They would have been 

 lacustrine except for the detrital filling, but were probably 

 fluviatile in the section below Utica. 



2 The Iromohawk river. This great river, draining Lake 

 Iroquois and the area of the Great lakes, was the predecessor of 

 the St Lawrence and was the equal of that river in size and 

 possibly in length of life. For some thousands of years it swept 

 the valley, trenching the rock barrier at Little Falls and grad- 

 ing its channel to that falling base level. The grade of the 

 river has been discussed [p. r34]. 



3 The Mohawk river, the present shrunken successor of the 

 Iroquois flood. 



It would be interesting if we could apportion with some 

 certainty the work of the three stages. It seems likely that the 

 work of the last stage, the present river, has been comparatively 

 small. The diminished river has cut only about 20 feet into 

 the channel which it found, and is meandering in a discouraged 

 and listless way over the broad plain of its gigantic ancestor. It 

 is unable to lower greatly for itself the rock barrier. But 

 between the effects of the first two stages the decision is not 

 so clear. The Glaciomohawk waters were large in volume and 



