S2 NEW YORK STATE MUSEUM 



north to south, or upstream. The cutting of the canyon progressed 

 downward from the top and from south to north. The upper 

 cataract was estabhshed first and independently before the lower or 

 deeper portion of the canyon had any existence. The down cutting 

 of the canyon proceeded only as the receiving waters (stages 6-8) 

 were lowered. The quantitative or progressive relationship of the 

 two factors is uncertain, but it is quite possible that the glacial 

 waters w^ere so long-lived that the canyon cutting kept pace with or 

 were even limited by the falling baselevel waters. 



This relation of river and lakes explains the existence of three 

 cataracts instead of only one, as would probably have been the case 

 if the river could have fallen freely through the whole distance from 

 Portageville to St Helena and the canyon cutting could have pro- 

 gressed normally and without vertical limitation. In rocks of 

 variable hardness or resistance a stream might alone develop multiple 

 cataracts, but the variation of the strata in the Portage section is 

 not sufficient to cause three cataracts with the spacing that now 

 exists. 



When the Portageville morainal lake came into independent ex- 

 istence by the fall of the broader glacial waters below the level of the 

 Erie Railroad viaduct plain, stream outflow began, probably at about 

 the position of the railroad viaduct. The fall of the stream, how- 

 ever, was limited by the level of the receiving waters, and during 

 the long life of the Dansville and Mount Morris-Geneseo lakes 

 (stages 6 and 7) the river work was restricted to the higher part of 

 the canyon. The lower part of the canyon, including the middle 

 and lower contracts, did not then exist, being covered and pro- 

 tected by the lake waters. The upper and south cataract was in- 

 dependently initiated and established, and probably receded some 

 distance, before the lower and northern part of the gorge had any 

 existence. Eventually the falling of the glacial waters through the 

 stages 6 and 7 brought the river into play in the horizon of the 

 middle cataract. 



As the crest of the third and youngest cataract is only about 850 

 feet elevation it is below the top of the High Banks canyon at Mount 

 Morris, and it is therefore evident that the lowest part of the 

 Portage canyon and the lowest cataract came into existence only as 

 the High Banks was cut. 



On account of the changes which have been produced subsequent 

 to the initiation of the cataracts and the withdrawl of the glacial 



