UPTILT OF LAND AT CLOSE OF ICE AGE 



345 



changes within the lake region which we now know to be with- 

 out warrant in the facts. Later it was learned that the uptilt 

 of the lake beaches is much accelerated to the northward (Fig. 

 373, B), and that new beaches make their appearance from be- 

 neath others as 

 we proceed in 

 this direction 

 there is a "feath- 

 ering out " of 

 beaches to the 

 northward (Fig. 

 373, C). 



The hinge 

 lines of uptilt. 

 Still later in 

 the study of the 

 region, it was 

 learned that the 

 axis or fulcrum 

 about which the 

 region has been 

 uptilted, instead 

 of lying to the 

 southward of the 

 lake district, as 

 had been as- 



FIG. 374. Map of the Great Lakes region to show iso- 

 bases and hinge lines of uptilt. a, isobase of the Chicago 

 outlet ; 6, main hinge line of the Lake Whittlesey beach 

 (Leverett) ; 6 1 , hinge line of the Lake Warren beach (Tay- 

 lor) ; c, isobase of the Port Huron outlet ; d, main hinge 

 line of highest Algonquin beach (Goldthwait) ; e, f, g, h, 

 additional hinge lines of Algonquin beaches in Door County 

 peninsula (Hobbs) ; I, isobase of the Lake Superior outlet 

 for the Algonquin beaches (Leverett) ; ra, isobase of the 

 same outlet for the Nipissing beaches (Leverett). 



sumed by Gilbert, lay within the region and about halfway up 

 the basin of Lake Michigan (Fig. 373, D, and Fig. 374). Simi- 

 larly, in the uptilt which followed the ice retreat in northern 

 Europe a definite hinge line of movement has been discovered. 



Lastly, it has been shown, as a result of the use of precise level- 

 ing methods, that not one but several hinge lines of movement 

 lie within the region, and that the separate sections into which 

 they divide the area are each in turn characterized by increased 

 up-cant as we proceed to the northward (Fig. 373, E and Fig. 374). 



The beaches of Lake Maumee, the earliest of the series of lakes 

 within the Huron-Erie lobe and within the extreme southern 

 portion of the Great Lakes area, show only the slightest possible 

 northerly uptilt, and the well-marked hinge line disclosed in the 



