SOUTHERN LIMIT OF UPLIFT 239 



"A part of this difference [of altitude] may be due to discrepancies between 

 the railroad surveys and a part to the difference in height to which the beach 

 was built above mean lake level. Thei^e elements of error and of variation 

 being eliminated, it is doubtful if enough difference will remain to require any 

 crust warping." " 



Similar statements are made by Lever ett with regard to the beach of 

 Lake Warren.^* 



The horizontality of the southern portion of a water-plane only 500 

 miles west of Lake Michigan was strongly suspected, indeed, as long ago 

 as the '80^s, when J. E. Todd and Warren Upham secured measurements 

 of altitude of the beaches of glacial lakes Agassiz and Dakota. In his 

 monograph on Lake Agassiz, Upham says, with reference to Todd's data : 



"It is evident . . . that the long area of Lake Dakota has experienced 

 only slight differential changes of level, at least in the direction from south to 

 north since the departure of the ice. The James River Valley is thus strongly 

 contrasted with the northern uplifting that has affected the Red River Valley, 

 as shown by the beaches of Lake Agassiz." " 



De Geer remarked, in 1892 : 



"As Prof. J. E. Todd and Mr. Upham have stated, the deserted shores of 

 Lake Dakota, situated close to the southwest of Lake Agassiz, show no or only 

 a slight unequal deformation. As the longer axis of this lake trends in nearly 

 the same direction as the greatest warping of Lake Agassiz, it seems probable 

 that the limit for this warping and at the same time for the upheaved area 

 lies just between Lake Agassiz and Lake Dakota, or through Lake Traverse." '' 



THE "HINGE LINE'' OR "I80BA8E OF ZERO" 



The line which separates the region in which a beach has been up- 

 warped from that in which it is still horizontal has been called by Lever- 

 ett a 'Tiinge line."^^ Because of its definite implication of warping on 

 one side and stability or uniformity on the other, this term seems prefer- 

 able to '^isobase for zero," which Avas used by De Geer. . The latter term, 

 unless qualified by a more definite phrase, allows the interpretation that 

 on one side of the line there has been differential uplift and on the other 



"Idem, p. 756. 



"Idem, p. 765. 



^^Upliam : The glacial Lake Agassiz. Monograph of the U. S. Geological Survey, vol. 

 25, 1895, p. 267. 



" De Geer : Proceedings of the Boston Society of Natural History, vol. 25, 1892, pp. 

 471-472. 



" This term was suggested to Mr. Leverett by the facts In the Erie basin, but has not 

 been used by him In print. It has been used by Coleman In a different sense, to mean a 

 node line drawn from an extinct outlet through points where a beach splits vertically 

 because of uplifts of that outlet. (See Coleman, Bulletin of the Geological Society of 

 America, vol, 15, 1904, p. 363.) 



