HalVs Remarks on Niagara Falls. Ill 



New York,"* By adopting this mode of explanation, we are 

 enabled to account for the existence of this and similar terra- 

 ces, alo^g the lines of bearing of our extensive limestone 

 formations, as well as for the deep valleys of ancient origin. 



The strata forming the escarpment at Lewiston, as seen in 

 the section, are those through which the chasm of the Niaga- 

 ra is excavated. The whole dip gradually to the south, and 

 all below No. 8, disappear below the level of the river before 

 reaching the falls, as may be seen by the dotted line bed which 

 represents the surface of the river below the falls. The strata 

 above this line are those excavated to form the channel of the 

 river. The limestone forming the summit of the terrace, and 

 at its margin not more than twenty feet thick, gradually in- 

 creases from the addition of higher layers, till at the falls it 

 has acquired a thickness of one hundred and twenty feet. 

 This limestone, about one mile south of the falls, disappears be- 

 neath the surface, and is succeeded by a soft marl of a bluish 

 or greenish grey color, with purple bands. This formation, 

 which is a continuation of the Onondaga saliferous group, 

 occupies all the level country from two miles south of the 

 falls, to Black Rock, a distance of eighteen miles by the 

 course of the river. This is succeeded by the water limestone 

 and Helderberg hmestone group. The saliferous formation, 

 occupying this great breadth of country, and forming an im- 

 portant item in any calculation regarding the recession of the 

 falls, has nevertheless always been overlooked by observers, 

 and its existence in that part of the country was never noticed 

 by any one, till the publication of the New York Geological 

 Reports, in 1838. Previously, all the distance between the 

 falls and Lake Erie was considered as underlaid by limestone ; 

 and the limestone of Black Rock, or the Helderberg group, 

 was placed immediately above the Niagara limestone, and 

 represented as resting upon it. 



The Niagara river, in its escape from Lake Erie, has exca- 

 vated a passage through the Helderberg limestone, (No. 10,) 

 which forms the upper terrace before noticed, leaving a small 



• Am. Journal of Science, Vol. XXXV. No I. 



