38 NEW YORK STATE MUSEUM 



only to remove some filling of drift and do a small amount of rock 

 cutting to produce the present pass. The rock shelves were probably 

 cleared of drift and exposed as we now find them (title 17, plates 

 13-25) by wave action of Lake Amsterdam waters. 



This fact is certain, that the Little Falls pass was cut to nearly its 

 present depth while the ice lay over Rome, and far antedating the 

 time when the flood from the Great Lakes poured through the valley. 

 We are compelled to the conclusion either that the trenching was 

 Prewisconsin or that the Mohawk drainage history connected with 

 the Wisconsin ice retreat is much more complicated than we can 

 now appreciate. 



THE DIVIDE AT ROME 



Closely connected with the problem of the rock pass at Little 

 Falls is that of the divide at Rome. It is a singular fact that the 

 col or divide at Rome, the place of outflow of Lake Iroquois, on 

 which headed for many thousand years a river as large as the St 

 Lawrence, is not rock but detritus, gravel, sand and clay. This lake 

 and stream deposit has a large area (see plate 2) and extends down 

 the Mohawk valley about 30 miles. Well borings at Rome (see title 

 5, page 190) show that the depth of these water-laid deposits is 

 considerable, in places over 100 feet. Brigham gives the rock 

 bottom at Rome as 320 feet, and at Little Falls 376 feet. It appears 

 that if the valley were cleared out to the rock the Mohawk river 

 would head at Little Falls and that a lake would occupy the ground 

 west of that point. 



It has long been recognized that in Preglacial time the drainage 

 divide was at Little Falls (see title 8, page 362) and that the water 

 west of Little Falls was tributary to a trunk stream in the Ontario 

 valley. It seems probable that in the earliest flow of the Glacio- 

 mohawk the stream headed at Little Falls while the valley westward 

 was occupied with quiet or lake waters, though it may have been 

 filled by glacial drift. However, any waters of the narrow lake 

 would have been soon displaced by the abundant detritus swept 

 in by the ice drainage and West Canada river and the conditions 

 changed from lacustrine to fluviatile. As the ice lobe melted back, 

 westward, the detrital filling probably followed it. 



The deep alluvial deposit at Rome, which now creates the divide 

 between St Lawrence and Mohawk drainage, is the delta built by 

 the heavy glacial drainage from the north and northwest during 

 Lake Amsterdam time (see plates 2, 15, 16). During all the life of 

 Lake Iroquois the detrital contribution of the upper Mohawk seems 

 to have been sufficient to block the outflow and to establish the 



