BOW THE GREAT LAKES WERE BUILT. 169 



Niagara Falls and the History of the Great Lakes, by the writer, 

 and published by the Commissioners of Niagara Falls Reserva- 

 tion, under the presidency of Hon. Andrew H. Green.* 



The Birth of the Great Lakes. This marks only an epi- 

 sode in the chain of events which are being described, when the 

 waters fell three hundred feet below the Algonquin and Lundy 

 planes. Although the subsidence of the waters was not continu- 

 ous and left some evidences of temporary pauses, yet the long rest 

 was not reached until they had sunk to the level of the Iroquois 

 beach. By this time the land had risen so high, and, as there were 

 no sufficient barriers, the upper lakes sunk far within their pres- 

 ent basins, as is shown on the map (Fig. 14). Still, the waters of 

 these upper lakes discharged by way of the narrow Nipissing 

 Strait. 



Lake Erie at this time had its birth, but then it was a very 

 small body of water, as shown on the map. The Niagara district 

 was then covered with a strait expanded into a lakelet, and after- 

 ward a river at first without a fall. In the further sinking of the 

 water to the Iroquois level the falls of Niagara commenced their 

 history, and then there was a comparatively long rest, but Onta- 

 rio was still a gulf, as shown on the map (Fig. 14). 



The plane of the Iroquois shore was at identically or nearly 

 the same level as the Nipissing beach (of Taylor) at the outlet of 

 Lake Huron by way of the Ottawa Valley. It is not apparent, 

 and it is theoretically improbable, that the Nipissing River was 

 characterized by more than a gentle slope, for by the time that 

 the land rose high enough to produce a rapid river the water of 

 the upper lakes had changed their outlet into Lake Erie. The 

 proof of these changes rests in the tilting of the beaches, which 

 aggregates several hundred feet (see Fig. 12). 



Barrier to Lake Ontario. Still, the land has continued to 

 rise, and the deformation since the Iroquois episode amounts to 

 more than before that date. The tilting at the head of Lake On- 

 tario becomes an absolute elevation above the sea, amounting to 

 three hundred and sixty-three feet, and at the northeastern corner 

 of the Adirondacks it is fifteen hundred feet, while near the outlet 

 of Lake Ontario it is seven hundred and thirty feet. This warp- 

 ing of the continent is illustrated in Fig. 15, and to it is due the 

 barrier (to a large extent) which retains the waters of the Ontario 

 basin at an elevation of two hundred and forty-seven feet above 

 the sea. 



Sinking and Subsequent Growth of the Modern Lakes 

 and Change of Outlets. The continuing elevation of the con- 



* The surveys of the deserted shore lines of the lakes have been mostly made by 

 J. W. Spencer, G. K. Gilbert, A. C. Lawson, and F. B. Taylor. 

 vol. xlix. 15 



