MODIFICATION OF THE (iREAT LAKES 2:57 



ing the St Marys river into existence, and eventually the present 

 condition was reacht. 



These various changes are so intimately related to the iiistt)ry 

 of the Niagara river that the Niagara time estimates, hased on 

 the erosion of the gorge by the cataract, can he applied to them. 

 Lake Erie has existed api)roximately as long as the Niagara 

 river, and its age should i)r()l)al)ly be reckoned in tens of tliou- 

 sands or hundreds of thousands of years. Lake Ontario is 

 much younger. All that can he said of the hegiiming of (Jreat 

 Lake Nipissing is that it came long after the beginning of liiike 

 Erie, but the date of its ending, through the transfer of outlet 

 from the Mattawa to the St Clair, is more definitely known. 

 That event is estimated by Taylor to have occurred between 

 5,000 and 10,000 years ago!* 



The lake history thus briefly sketcht is characterized by a prt)- 

 gressive change in the attitude of the land, the northern and 

 northeastern portions of the region becoming higher, so as to 

 turn the waters more and more toward the southwest. Tlie 

 latest change, from Great Lake Nipissing to Great Lakes Supe- 

 rior, Michigan, and Huron, involving an uplift at the north of 

 more than 100 feet, has taken place within so short a period 

 that we are naturally led to inquire whether it has yet ceast. Is 

 it not probable that the land is still rising at the north and the 

 lakes are still encroaching on their southern shores? .1. W. 

 Spencer, who has l)een an active explorer of the shore-lines of 

 the glacial lakes and has given much study to related i>roblems, 

 is of opinion that the movements are not comi)lete, and predicts 

 that they will result in the restoration of the Chicago outlet of 

 Lake Michigan and the drying of Niagara.! 



The imi)ortance of testing this question by actual measure- 

 ments was imi)rest uj)on me several years ago, and I endeavored 

 to secure the institution of an elaborate set of observations to 

 that end. Failing in this, I undertook a less expensive investi- 

 gation, which began with the examination of existing records 

 of lake height as recorded by gage readings, and was continued 

 by the establishment of a number of gage stations in l.Sl>6. To 

 understand fuUv the nature of this investigation it is necessary 

 to consider the difficulties that arise from tlie multifarious mo- 

 tions to which the lake water is subject. 



, studies in Indiana Geo«raph.v. X. A short history of the Oro.u L.k- l-rro 

 Haute, 1897. 

 t Proc. Am. Ass. Adv. Sci., vol LIII, 1894, p. 240. 



