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THE GEOLOGICAL HISTORY OF NEW YORK STATE TOQ 
by ice erosion, and during the Algonquin-Iroquois stage of the 
Great Lakes history, we have learned that these lakes discharged 
through the Mohawk valley and across the Little Falls divide. It 
was the passage of this great volume of water over the divide 
which caused the cutting of most of the gorge as we now find it, 
except for the narrow trench in the hard, underlying Precambric 
rock which is no doubt due to postglacial erosion. During the 
Iroquois stage an arm of the lake extended along the valley from 
Rome to Little Falls. All the streams from north and south which 
entered this arm of the lake were heavily charged with debris from 
the newly drift-covered regions and, the current not being strong 
enough to carry away the debris, the valley from Rome to Little 
Falls was built up (aggraded) to such an extent that, after the dis- 
appearance of Lake Iroquois, the drainage from Rome was able to 
continue eastward. Thus we have here a very fine example of 
exact reversal of drainage directly due to glaciation and by this 
means the upper waters of the Mohawk were added to the pre- 
glacial Mohawk. 
Closely associated with the above is the postglacial history of 
West Canada creek and the famous chasm at Trenton Falls. The 
preglacial West Canada creek flowed from Prospect (upper end 
of Trenton chasm) past Holland Patent, through the valley of the 
present Nine Mile creek, and into the Rome river opposite the 
village of Oriskany. This channel was completely blocked by 
glacial drift at Prospect so that the creek was forced to find a new 
course southward over the limestone at Trenton Falls, and thence 
southeastward to its present mouth at Herkimer. The gorge, be- 
tween Prospect and Trenton Falls villages, is 214 miles long and 
from 100 to 200 feet deep, and has been cut into the Trenton lime- 
stone by the postglacial stream. It contains five or six waterfalls 
ranging in height from 10 to 126 feet, the total drop of the water 
in the 2%4 miles of the gorge being 360 feet (see plates 43 and 44). 
In the southeastern Adirondacks, the upper waters of the Hudson 
tiver present some very interesting examples of drainage changes. 
In fact, it is not too much to say that the larger drainage features 
of that region have been well nigh revolutionized as a result of 
glaciation. The accompanying sketch map (fig. 37) gives a fair idea 
of the changes, but reference to the State geologic map and to the 
topographic maps of the region is greatly to be desired. The State 
geologic map shows two distinct embayments of Paleozoic rocks 
forming valleys which extend northward, one to Northville and 
the other to Corinth, and into the mass of Precambric rocks of the 
