10 



in more detail and represented on a larger scale, anothei 

 less pronounced cuesta and lowland are found to lie 

 between, and their relations to Niagara history increase 

 their present importance. These are the Onondaga 

 cuesta, formed on the outcropping ledges of the Onon- 

 daga limestone, and the Huron or Tonawanda lowland 

 north of it. The Tonawanda and Chippawa valleys 

 and the deeper trough of Lake Huron are in this lowland. 

 This division of the belted area restricts the application 

 of the name Erie lowland to the lowland belt which lies 

 south of the Onondaga escarpment and in which lies the 

 bed of Lake Erie. In the early history of Niagara river 

 the Tonawanda lowland was occupied by a temporary 

 lake about 50 miles (80 km.) long and I to 7 miles 

 (i-6 to 11-3 km.) wide. Lake Tonawanda covered the 

 lower ground around the city of Niagara Falls and extended 

 east about 40 miles (64 km.) and west 10 miles (16 km.) 

 into Canada. 



ORIGIN OF DRAINAGE SYSTEM. 



In the early development of drainage on the newly 

 elevated coastal plain, the master streams probably flowed 

 south or southwest over the Great Lakes region and were, 

 as Grabau has said, consequent streams, their course being 

 determined by the direction of the original slope. Subse- 

 quent streams began immediately cutting valleys along 

 the lines of the weaker strata at right angles to the main 

 streams, and these side streams ultimately combined and 

 developed a system which became dominant. The 

 final stage in which the deeper lake basins were excavated 

 and the land surface prepared for the Great Lakes and 

 for inter-glacial Niagaras, as well as the modern Niagara, 

 was probably accomplished chiefly after the original 

 drainage system had been broken up and had ceased to be 

 dominant. 



STRATA IN NIAGARA GORGE. 



The ancient belted plain, with its parallel features of 

 relief, was the ground over which Niagara river began to 

 flow when it first came into existence, and it is into this 

 plain that the cataract has sawn the great canyon. North 

 of Lewiston there was no capping hard layer to produce 



