UPTILT OF LAND AT CLOSE OF ICE AGE 349 



basins. This should, however, be true only of basins whose 

 outlets are to the northeastward of the existing main hinge line 

 of uptilt. Lake Huron, having its outlet at the southern margin 

 of its basin, should not have its waters encroaching upon the 

 southern shore, for the simple reason that any continued uptilt 

 of the basin can only have the effect of pouring more water through 

 the outlet. Lake Michigan and Saginaw Bay, which are arms of 

 the Huron basin, ought, however, to become flooded upon their 

 southern shores, were it not that the hinge line of uptilt to-day lies 

 to the northward of the outlet at Port Huron, and, further, that the 

 two connecting channels still have their beds lower than the sill of 

 the outlet channel. Now the evidence goes to show that no en- 

 croachment of waters is occurring upon the Chicago shore of Lake 

 Michigan, and although the shores of Saginaw Bay are so exces- 

 sively flat as to reveal slight changes of level by large migrations 

 of the strand, yet the ancient meander posts fixed by the early 

 surveys are still found near the water's edge. 



Drowning of southwestern shores of Lakes Superior and Erie. 

 Within the basins occupied by Lakes Superior and Erie, a wholly 

 different condition is found. In each case the outlet is found 

 to the northeastward (Fig. 374, p. 345), and the northwesterly trend 

 of the isobases from these outlets is responsible for a continued 

 elevation from uptilt of the outlets with reference to the western 

 and southern shores. In consequence, the waters are encroach- 

 ing upon these shores, and rivers which there enter the lake are 

 drowned at their mouths, with the formation of estuaries. Upon 

 Lake Superior these changes are very marked near Duluth and par- 

 ticularly in the St. Louis River, within which, since the early treaty 

 with the Indians, certain rapids have disappeared and submerged 

 trunks of trees are now found in the channel of the river. As 

 far east as Ontonagon essentially the same conditions are found. 



Upon the shores within the Porcupine Mountain district, the 

 waters are clearly rising. Here old cedar trees may be seen, in 

 some cases dead but still upright and standing in from six to eight 

 inches of water a number of feet out from the present shore, 

 while others near the shore, but upon the land and still living, are 

 washed by the waves, and losing their lower bark in consequence. 

 An old road along the shore has had to be abandoned because of 

 the encroaching water. 



