'20() II. L. FAlRCHlLi:) POST-GLACIAL LPLIFT OF N. E. AMERICA 



til is oxtremelv difficult, but interesting pro1)lcm, tlie altitude relation of 

 the hypothetical change of water level to the ])ost-Glacial land uplift may 

 be briefly outlined. 



Assuming an effective rise of the ocean level, due to the return of the 

 glacier water to the sea, the following conditions seem imperative or 

 liiglily probable: 



1. The rise of ocean level (flooding) was proportional to the waning 

 of the glaciers, and was contemporaneous, not subsequent. 



-!. In at least the peripheral portion of the uplifted area the rise of the 

 land was subsequent to the removal of the ice (unloading) from such 

 area. 



:]. The land uplift was by a progressive wave movement. 



4. Toward the center of the glaciated area the wave of uplift might 

 have overtaken the slowly receding margin of the diminished ice-body, 

 so that some uplift occurred beneath the ice-sheet while the sea was yet 

 excluded from the district, the sea being nearly restored to full height. 



From the aljove conditions the following conclusions are derived : 



(a) About the borders of the uplifted area, where the rise was small, 

 diminishing to zero, and where the ocean flooding was the maximum, the 

 primitive shore features are all submerged. 



(h) The primitive marine shore features at any point are now above 

 the present (flooded) sealevel only where the total land uplift has ex- 

 ceeded the rise of the ocean, which occurred subsequent to the beginning 

 of the uplift at that point. 



(c) Therefore the total land uplift at any point is the present apparent 

 and measuralde height above the sea plus the vertical amount of ocean 

 flooding subsequent to the initiation of land uplift at that point. 



The above conclusions may be restated in the following generalizations : 



(A) Except at the center of the uplifted land area, the total amount 

 of land uplift is everywhere greater than the apparent rise. 



(B) The amount of marine flooding is maximum at the periphery of 

 the glaciated area and declines to zero at the center. 



(C) Conversely, the apparent or visible uplift, like the total uplift, 

 is greatest at the center of the area and diminishes toward the margin. 



The immediate practical application of the above conclusions may not 

 be unimportant. As the datum level for all land uplift is the ^^resent 

 sea surface, it is not feasible to determine the amount of iion-apparent 

 or flooded rise of the land; but the relation of the apparent uplift to 

 the glaciated borders, as indicated Iw the map, may be significant. 



The only locality east of the Hudson Yalley where the terminal mo- 

 raine lies on the land is Lono- Island. At the middle of the Island the 



