JuxE, 1930 



EVOLUTION 



Page eleven 



lis 



Goat Island 

 Panoramic Summer View of Niagara Falls from Canadian Side of Gorge 



Horseshoe Fall 



when the ice retreat 

 rd outlet for the up- 



the Trent River of 



Niagara of all but 

 g a mere 15 percent 



So for tlie next mile 

 ing was slow though 

 g gorge being both 

 r, now evident from 

 r of the constricted 



north and east was 

 ief as the heavy ice 

 effect was to lift the 

 IS to cut it off and 

 aters again through 

 r the Niagara brink, 

 iplift of the Mohawk 

 fork, through which 

 ned. Their level was 

 icked up the Niagara 

 le fall and prevented 

 the rather resistant 



This portion of the 

 t wide, but originalh' 

 iver has since rasped 

 igh the old sandstone 

 le receding ice sheet 

 rence valley and the 

 I again fell, of course 

 outlet and restoring 

 unging falls, cutting 



During this third stage the Whirlpool 

 was formed. In pre-glacial times, a river 

 had flowed across this region toward St. 

 David. It too had a great waterfall that 

 had cut its gorge upstream as far as the 



o o Q o o o 



Q Q O Q Q O -, 



Sketch Map of >'iagara Gorge 

 Depth of water shown in black 



Kindle and Taylor 



present Whirlpool. But the last ice invasion 

 liad buried this gorge under a ma.ss of clay 

 and gravel. Once the receding Niagara 

 Falls reached tliis ancient gorge, it swiftly 

 cleared out the softer filling in its path, 

 leaving tlie deo}) Whirlpool basin. 



Tiie fourth stage began when the receding 

 ice sheet uncovered a low outlet for the up- 

 per Great Lakes bj' way of the Ottawa River 

 of Canada, again robbing Niagara of all 

 but the Erie waters. The weakened falls 



cut only a shallow and narrow gorge and 

 could not even sweep away the boulders 

 fallen from its brink. So today, the water 

 rushes througii this encumbered and con- 

 stricted channel as the furiously tumbling 

 Whirlpool Rapids. 



Finally the present stage was inaugurated 

 by a further uplift of the land to the north, 

 cutting off the Ottawa outlet and again 

 sending the Great Lakes waters by way of 

 Erie and Niagara. The restored falls then 

 began to cut the present deep upper gorge. 

 An angle in the river bed permitted the re- 

 cent splitting of the falls into the American 

 and Canadian falls, with Goat Island be- 

 tween. Much the greater volume of water 

 flows over the Canadian falls which are 

 therefore receding rapidly, the American 

 falls being too feeble to remove the rock 

 debris at its base, w'hich prevents the under- 

 mining necessary for speedy recession. The 

 face between the two falls is therefore very 

 unequal and the time is coming when the 

 Canadian Falls, receding past the head of 

 Goat Island, will cut off all water from the 

 American side, leaving the dry upper river 

 channel and abandoned fall scarp. 



A similar event occurred during the third 

 recession stage at Niagara Glen, its aban- 

 doned fall scarp and upper river channel 

 being however on the Canadian side. Here 

 one may wander through tlie dry river above 

 and among tiic boulders strewing the gorge 

 below the precipitous brink of a once mighty 

 waterfall. 



It will be seen that Niagara has had an 

 eventful development and that changes of 

 volume quite prevent us from using the pres- 

 ent recession rate of four feet per year to 

 estimate the ago of the falls themselves and 

 the dates of the ice sheet retreat. But care- 

 hil consideration of the factors involved 

 and other quite independent data lead us to 

 estimate a total age of between 30,000 and 

 3-5,000 years for tiie falls since they started 

 from the Lewiston brink. 



Reference: The Falls of Niagara, Glenn 

 C. Forrester, N. Y. 1928. 



