22 NEW YORK STATE MUSEUM 



Geologic map 



A few words, descriptive of the accompanying geologic map may 

 be added. 



The topography is indicated chiefly by contour lines. These 

 lines are 20 feet apart, and each connects the points which have the 

 same elevation above sealevel. Thus wherever the 300 foot con- 

 tour line occurs, every point along that line is supposed to be 300 

 feet above sealevel. The level of Lake Ontario is 247 feet above 

 the sea; therefore the hight of any point above Lake Ontario can be 

 calculated from the contours. Where the contours are close 

 together, the slope of the country is steep; where far apart, it is 

 gentle. 



The various color patterns indicate what geologic formations 

 would be shown on the surface of any given area, if the drift cover- 

 ing were removed. The beds of this region all dip gently south- 

 ward; and, as we proceed northward, the lower beds rise from 

 beneath the covering of the higher. Where steep cliffs occur, as 

 in the gorge of the river or at Lewiston or Queenston, the lower 

 beds crop out beneath the upper ones for only a very short, space ; 

 hence they appear on the map as narrow color bands only. The 

 character of the outcrops in the buried St Davids channel is only 

 approximately delineated, to the extent indicated by well borings. 

 It is probably much more irregular than is shown. 



The outlines of the edges of the various beds from Lewiston east- 

 ward are taken from a map by G. K. Gilbert, the man who more 

 than any other is identified with geologic studies at Niagara. The 

 outcrops of the Onondaga and waterlime beds are taken from a map 

 by Prof. I. P. Bishop. For the other outlines the author ii responsi- 

 ble. 



A few statistics 1 



Hight of American falls, Oct. 4, 1842 167.7 ^ eet 



" Horseshoe falls, " 2 i58. 5 

 Mean total recession of American falls between 1842 



and 1890 30.75 



Chiefly from the annual reports of the commissioners of the state- 

 reservation. 



"The hights vary from 4 to 20 feet with the elevation of the water in 

 the river below the falls. 



