DISCUSSION OF THE MAP 203 



Taylor's ^^ Whittlesey Hinge Line," his zero of land uplift, lies 250 miles 

 north of the ice limit of the Wisconsin stage and 350 miles north of the 

 extreme glacial limit (80, figure 14, page 503), and it has no reference 

 to the ice lobations. The thickness of the ice at this line was 3,000 to 

 4,000 feet (80, page 511). It would appear more probable that some 

 combination of wave uplift with the lake history has left the southern 

 beaches with small deformation than that such great thickness and extent 

 of the ice had no diastrophic effect. 



The map shows that the post-Glacial land uplift of northeastern Amer- 

 ica is fairly proportionate to the area and thickness of the latest ice-sheet, 

 and it appears legitimate to suggest similar relation in the Mississippi 

 and Great Lakes region. The southward curve given to the lower-value 

 isobases may be excessive, but they suggest an uplift for which evidence 

 should be sous^ht. 



It should be understood, therefore, that the isobases as extended in the 

 Mississippi Basin are intended to be only suggestive of the southerly limit 

 of the Pleistocene land uplift, and that the lines of the rest of the map, 

 east of Michigan and Ohio, indicate the total rise of land during and 

 following the removal of the latest, or Labradorian, ice-cap. 



The location of the central area of uplift between Quebec City and 

 James Bay agrees with the conclusions reached many years ago by J. W. 

 Spencer, using a different method. He located the area of maximum 

 uplift by triangulation on points of the deformed shorelines. As early 

 as 1889 he summarized his conclusion as follows: 



"At any rate, it is in tlie reg:ion southeast of James Bay that the maximum 

 differential elevation of the earth's crust, which involved the Iroquois Beach, 

 is to be found." ^ » 



And in 1913 he wrote as follows : 



"By triangulating: the Iroquois, Algonquin, and other beaches, the dome of 

 the greatest deformation of the Great Lakes region is found to be situated 

 approximately in latitude 50° 30' north, longitude 75° west. This is confirmed 

 by the course of the drainage of the highlands. It is the locality where the 

 'height of land' reaches its most southern lobe" (79, page 227). 



The map also suggests that the latest ice-sheet on North America would 

 more appropriately liave been named from Quebec instead of Labrador. 



Over Labrador the isobases have been adjusted with particular refer- 

 ence to Professor Daly's figures for the raised beaches along the north- 

 cast coast (39). His study seems to locate fairly the 300- and lOO-foot 



■■■• 'IM-juisjuMions of llic Uoyal Society ol' (^auadti, vol. 7. l.Ssn. p. rjn. .Fouriuil of (Jct.l- 

 ogy, vol. 10, 11)11, p. HT. 



