THE QUATERNARY PERIOD 



353 



is certain that typical, steep-sided, narrow gorges, as well as 

 waterfalls, must have been very uncommon, if present at all. 

 Like lakes, such fea- 

 tures are ephemeral, 

 because, under our 

 conditions of climate, 

 gorges soon (geolog- 

 ically) widen at the 

 top, and waterfalls 

 disappear by retreat 

 or by wearing away 

 the hard rock which 

 causes them. 



Changes of stream 

 courses are also nu- 

 merous in many parts 

 of the glaciated ter- 

 ritory. It is the pres- 

 ent purpose to de- 

 scribe only a few 

 typical, well-studied 

 cases of such stream 

 changes. 



From the stand- 

 point of both geology 

 and human history, 

 the gorge at Little 

 Falls (on the New 

 York Central R. R.) 

 in central New York 

 is the most impor- 

 tant in that state. 

 Before the Ice age 

 there was a divide 

 instead of a gorge 

 several hundred feet 

 above the present 



river level. The Mohawk River flowed eastward, and the now 

 extinct Rome River flowed westward from that divide (see Fig. 

 221). During the Algonquin-Iroquois stage of the Great Lakes 



Fig. 222 

 Sketch map of the southeastern Adirondack 

 region, showing the relation of the pre-Glacial 

 drainage to that of the present. Pre-Glacial 

 courses shown by dotted lines only where es- 

 sentially different from present streams. (After 

 W. J. Miller, Bui. Geol. Soc. Amer., vol. 22.) 



