312 



SCIENCE. 



[Vol. XIX. No. 487 



EEVIEW OF THE ORIGIN OF THE BASINS OF THE 

 GREAT LAKES/ 



The origin of such promiuent features as the Great Lakes 

 has a general interest to others as well as to geologists; but 

 even phenomena so commonplace are not always readily ex- 

 plained. The delay iu this case has been largely due to the 

 want of information that could only be obtained by uumei'ous 

 borings, accurate levelling, and other data obtainable in 

 regions where few active workers in surface geology have 

 been carrying on their investigations. To these causes may 

 be added a quasi satisfaction with favorite theories, to which 

 facts are often moulded. 



A score of years ago the mysterious agent which formed 

 the lake basins assumed the guise of glaciers digging out 

 new troughs or fashioning older ones. This plausible hy- 

 pothesis received consideration, as it was championed by Dr. 

 J. S. Newberry and other eminent men. At that time, and 



merged in them These phenomena were first emphasized 

 in America by Dr. J. W. Spencer, and were sufficient to 

 disprove the hypothesis, even if no other had been available. 



The amount of glacial erosion demanded was more than 

 could be accepted by many glacialists. Accordingly Dr. T. 

 C. Chamberlin accounted in part for the lake basins as 

 due to depressions produced by glaciers accumulating to a 

 greater thickness over preglacial valleys, but that with the 

 retreat of the glacier the waters left iu the basins still de- 

 pressed the earth's crust. The demonstration of such a 

 theory could scarcely be hoped for. It not only begged the 

 question, but in doing so it did not consider that the pre- 

 vious removal of the hundreds of feet of rock, in forming 

 the accepted valleys, ought to have permanently produced 

 the opposite effects upon the earth's crust to that of the 

 small quantity of water left in the basins, especially as the 

 basins were sometimes shallow and sometimes channel-like. 



These theoretical explanations showed the necessity for 



for years after, the extraordinary erosive power of glaciers, 

 in scooping out basins, was an article of faith; but to-day 

 few observers of existing glaciers, or of real extinct ones, have 

 DOt modified this old creed, as observations do not support it. 

 Apart from the question of the ability of ice to plough out 

 great basins, the direction of the ice scratches about the 

 Great Lakes is oblique, or often at right angles, to the es- 

 carpments or rock walls which bound the lakes, or are sub- 



' " High Continental Elevations Preceding the Pleistocene Perloi (la 

 America)," with map. Head belore Geo!. Soc. Am., Aug., 1889. Bull, of Soc, 

 TOl. 1. Geological Magazine (London), dec. HI., vol. vil., 1890. 



" Origin of the Basins of the Great Lakes," with map of the Ancient St. Law- 

 rence River and Tributaries. Quar. Jour. Geol. Soc. (London), vol. xlvl., 1890. 

 Keprlnted In American Geologist, vol. Iv., 1891. 



" Deformation of the Iroquois ijeach and Birth of Lake Ontario," with map 

 and illustrations. Am. Jour. Sci., vol. si., 1890. 



" Deformation of the Algonquin Beach and Birth of Lake Huron," with map 

 and Illustrations. Am. Jour. Scl., vol. xU., 1891. 



"High-Level Shores In the Eeglon of the Great Lakes, and their Deforma- 

 tion," with map. Am. Jour. Sci., vol. xll., 1891. 



" Post^Plioceue Continental Subsidence," with map of deserted Short-Lines 

 n the region of the Great Lakes. Read before Geol. Soc. Am., Dec, 1890. BuU. 

 of Soc, vol. 11. 



further research, which has been made by Dr. Spencer with 

 results announced from time to time for more than a decade, 

 and may be summarized as follows: The lake basins are 

 simply valleys of erosion, formed during periods of high 

 continental elevation lasting long enough for the excavation 

 of broad, deep valleys. This elevation amounted to 3,000 

 feet above the present altitude, as shown by the submerged 

 channels upon the coast; and temporarily the continent ap- 

 pears to ihave reached even 6,000 feet. Some of the lakes 

 now descend to nearly 500 feet below sea-level. The basins 

 of the lakes were just such broad valleys as that of the mod- 

 ern St. Lawrence River north of the Adirondacks or farther 

 seaward. During the later geological times, and reaching 

 down to the modern days, the physical revolutions of the 

 Ice Age converted the old valleys of the St. Lawrence (Law- 

 rentian) River and its tributaries into basins, in which the 

 modern lake waters are held. The phases of the physical 

 revolutions which fashioned the basins were partial obstruc- 

 tion of the old waterways by drift accumulations, a general 



