II 



a vertical fall; the banks are composed of soft red shale 

 and are relatively low. The gorge begins at the escarpment 

 south of Lewiston. From this place to the present falls 

 the arrangement of the strata favoured the continuous 

 existence of a vertical cataract, except at the Whirlpool 

 which was filled with loose glacial drift. The hard, massive 

 bed of the Lockport (Niagara) limestone forms the capping 

 layer and increases in thickness from less than 20 feet 

 (6- 06 m.) at the escarpment to about 80 feet (24 m.) 

 at the Horseshoe Falls, 130 feet (40 m.) at the first 

 cascade above the falls and about 250 feet (76 m.) 

 in well borings farther south. At the lower levels the 

 Clinton limestone, with the Medina (upper Medina) 

 sandstone close below and the Basal or Whirlpool sandstone 

 of the Cataract (Medina) formation are hard, but they 

 are relatively thin. The rest of the strata are mainly 

 soft shales, but with occasional thin, sandy, harder beds. 



The strata through which the gorge is cut appear 

 to the eye to be horizontal, but in reality they dip toward 

 the south at a nearly uniform rate of 20 feet to the mile 

 (3-8 m. per km.). There are slight variations from this 

 rate, most notably near the mouth of the gorge, where 

 the dip for some distance is slightly greater. From the 

 mouth of the gorge to the Horseshoe Fall all of the strata 

 decline southward 130 to 140 feet (36-6 to 42-7 m.). 



The next important hard layer below the Lockport 

 is the Clinton limestone which is about 20 feet (6 m.) 

 thick and forms a distinct bench along the sides of the 

 gorge at some places. Spencer, finds only 12 feet (3-6 m.) 

 of the Clinton limestone above water at the Horseshoe 

 Fall. At Foster's flats the Clinton forms the prominent 

 bench next below Wintergreen terrace and many of the 

 great, fallen blocks rest upon it. 



The only other hard layer of importance is the Whirl- 

 pool sandstone, which is oh the average about 25 feet 

 (7-6 m.) thick. At the mouch of the gorge the top of 

 this sandstone is 142 feet (43-3 m.) above Lake Ontario. 

 At Foster's flats it is about 75 feet (23 m.) above the 

 lake and forms the floor of the flats and of Niagara glen 

 and its bottom is at the waters edge at the head of Foster 

 rapids. At the whirlpool it forms a bench a few feet 

 above the water and is most accessible on the east side 

 below Whirlpool point. Farther south it passes beneath 

 the level of the river. The surface at the whirlpool 



