National Geographic : 1897 Sep
MODIFICATION OF THE GREAT LAKES ing the St Marys river into existence, and eventually the present condition was reacht. These various changes are so intimately related to the history of the Niagara river that the Niagara time estimates, based on the erosion of the gorge by the cataract, can be applied to them. Lake Erie has existed approximately as long as the Niagara river, and its age should probably be reckoned in tens of thou sands or hundreds of thousands of years. Lake Ontario is much younger. All that can be said of the beginning of Great Lake Nipissing is that it came long after the beginning of Lake 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 pro 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. The 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? J. W. Spencer, who has been an active explorer of the shore-lines of the glacial lakes and has given much study to related problems, is of opinion that the movements are not complete, and predicts that they will result in the restoration of the Chicago outlet of Lake Michigan and the drying of Niagara.t The importance of testing this question by actual measure ments was imprest upon 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 1896. To understand fully the nature of this investigation it is necessary to consider the difficulties that arise from the multifarious mo tions to which the lake water is subject. *Studies in Indiana Geography, X. A short history of the Great Lakes. Terre Haute, 1897. t Proc. Am. Ass. Adv. Sci., vol. LIII, 1894, p. 246.