LOS NEW YORK STATE MUSEUM 
Drainage changes, aside from those already described in con- 
nection with the history of lakes, are also numerous in New York. 
It must be remembered that, with few exceptions (for example, the 
basins of Lakes Ontario and Erie, Niagara river, and possibly the 
St Lawrence river), the major drainage lines of the State were 
little changed during the Ice age because the principal valleys were 
mostly the same before and after glaciation. It is the present 
purpose briefly to describe only some of the most important and 
best known cases of stream changes due to the Ice age.’ - 
From the standpoint of both geography and human history, the 
gorge at Little Falls is the most important in New York State (see 
figure 7 and plate 42 and also the description in chapter 2). Before 
the Ice age there was a divide, instead of the gorge, several hun- 
dred feet above the present river level, which consisted of hard 
Little Falls dolomite. The prominence of this rock barrier was 
greatly increased by the tilting of the strata due to the development 
of the Little Falls fault. The Mohawk river flowed eastward, and 
the now extinct Rome river flowed westward, from this divide (see 
figure 36). During the Ice age the divide was somewhat lowered 
Movrisviile 
Richfield 
nee 
p 
Fic. 36 Sketch map of central New York, showing the relation of pre- 
glacial to postglacial drainage. Preglacial streams shown by dotted lines only 
where essentially different from existing streams. 
Based upon work of A. P. Brigham 
1All the drainage changes now to be described will be much better under- 
stood by consulting the large government topographic maps of the regions 
considered. 
