J. W. Spencer — Duration of Niagara Falls. 457 



long and varies from 900 to 1400 feet in width (see fig. 1 and 

 sections). After the river issues from the gorge its width is 

 about a half a mile, and the depth reaches to 96 feet, or 94 

 feet below the surface of Lake Ontario. In the canon, three 

 quarters of a mile below the site of the falls, the river has a 

 depth of 189 feet, at a point where the surface is about 105 

 feet above the lower lake. That the upper part of the walls of 

 the canon are vertical should be emphasized. 



3. Geology of the District. 



The geology of the district is too well known to need 

 description, but the measurements had not been made which 

 could be used in determining the varying character of the 

 work performed by the river ; accordingly I made the follow- 

 ing sections and those illustrated in figures 3, 6, 7, 8, 9, 10, 11. 





At Falls. 



Whirlpool 



Devil's Hole. 



N. Cath. Col. 



End of 



OOKGE. 





Feet 

 thick. 



160 



55 



60 



15-20 



20-15 



Ft.ab've 

 L. Ont. 



Feet 

 thick 



40* 

 65 

 65" 

 20 



25 

 8 

 30 

 20 

 40 



Ft.ab've 

 L. Ont. 



Feet 

 thick. 



Ft. ab've 

 L. Ont. 



Feet 

 thick. 



Ft.ab've 

 h. Ont. 



Feet 

 thick. 



Ft. ab've 

 L. Ont. 



Pleistocene in depressions 

 and on ridges 



Niagara limestone 



Crest of Falls 



Niagara shale . 



440 



280 

 270 

 225 



165 



110 



100 

 60 



340 

 300 

 235 

 270 

 15-20 



105 

 60 



(30? 



340 

 250 



<35H 

 60 

 20 

 20 



340 

 265 

 205 



jlSft 



)25$ 

 75 



15 



20 



20 



5 



25 



20 



120 



- — 1 



340 

 300 



Clinton limestone. 



Bands of shale, limestone 



and sandstone at base. 



Surface of river 



225 



Medina shale 



25 

 5-10 

 30 

 20 

 40 





sandstonet 



shale 



170 



sandstone 



shale to lake level 



140 



The plain between the escarpment and Lake Ontario is 

 underlaid by a great thickness of Medina shales thinly cov- 

 ered with drift and lacustrine deposits. The flat country, 

 between the head of the rapids above the falls and the De- 

 vonian escarpment near Lake Erie is underlaid by shaly rocks 

 of Onondaga age. The southward dip of the strata from the 

 end of the gorge to the Devil's hole (9,700 feet distant, at the 

 mouth of Bloody run) is 40 feet ; thence to the whirlpool 



* Drift on west side, rocks on east side of gorge. 



f The upper figures relate to rocks in river terrace ; the lower in walls of gorge. 



\ Both the Medina sandstone and shales vary in thickness. 



