NIAGARA FALLS AND VICINITY 55 



Chapter 2 



LIFE HISTORY OF NIAGARA FALLS 



Glacial period 



Two important events immediately preceded the birth of Niagara. 

 The first was the formation of a series of great lowlands and cuestas 

 by stream and atmospheric erosion during a period of time when, 

 according to all indications, the land stood from 2000 to 5000 feet 

 higher than it does now. This was outlined in the preceding chap- 

 ter. The second event was the accumulation of a great mantle of 

 glacial ice over most of northeastern North America, and the modi- 

 fications of the previously formed erosion topography, either by the 

 erosive action of the ice or by deposits left on its melting. The 

 time equivalent of the latter event is commonly known as the 

 glacial period of the earth's history, a remote period as time 

 is ordinarily counted, but a very recent one in the chronometry 

 of the geologist. Contemporaneous with this great accumulation 

 of ice was probably the subsidence of the northern part of this 

 region, thus changing the slope of the land surface from a south- 

 ward to a northward one. 



The greatest accumulation of ice during the glacial period appears 

 to have been in the region to the north and northeast of the great 

 lakes, or in general over the area of the Laurentian old-land. The 

 immediate causes which brought about such accumulation, were the 

 extensive refrigeration of the climate and the increased precipitation 

 of moisture, so that a greater amount of snow fell during the winter 

 seasons than could be removed by melting during the succeeding 

 summers. The partial melting and refreezing of the snow, which 

 continued over a long period of time, eventually resulted in pro- 

 ducing glacier ice, after the manner of the formation of glaciers at 

 the present time. 



The thickness of the great Laurentian glacier, which eventually 

 covered all the land of this region, including even the highest moun- 

 tains, must be estimated at thousands of feet in its central part with 

 a progressive diminution of thickness toward the margin. The ice 



