THE HI8T0RY OF THE NIAGARA RIVER. 



251 



Plate VII. — Chart of the Ciavf Line at the head ok the JSiagai:a 

 Gorge, compiled to show the Recession from 1842 to 1886. 



Explanation. — Broken liue, crest of falls and cliflF as mapped by N. Y. State Geol. Survey in 

 1842. Full line, cre.st of falls as mapped V)y tlie U. S. Geol.'Siirvey iu 1886, with other fea- 

 tures as mapped by the U. S. Lake Survey in 1875. 



