550 KIRTLEY F. MATHER 



relations between the fossil-bearing clay zones in the vicinity of 

 Ottawa. 



The quaternary deposits near Waterville, Maine, suggest a 

 similar movement of the sea-level there. H. P. Little 1 states that 

 "the main mass of the fluvio-glacial deposits is found in an esker 

 .... bordered by marine clays and sands. These overlap the 

 esker and are separated from its gravels by an unconformity con- 

 sidered due to sub-aerial erosion." 



CHANGES IN SEA-LEVEL INCIDENT UPON THE WASTING OF THE 

 LABRADORIAN ICE SHEET 



The suggestion is an obvious one that the positive movement 

 of the strand line in late Pleistocene times in Northwestern North 

 America may be a result of the return of water to the ocean basins 

 from wasting ice caps. The simple effect of ice melting is, however, 

 complicated in the region under discussion by close proximity to the 

 ice masses. Here, too, sea transgression has been followed by a 

 presumably much greater negative movement of the strand, which 

 has continued nearly or quite to the present time. Barrell's 2 

 discussion of the various problems involved is especially stimulating 

 in this connection. 



Three factors enter into the local problem: elevation of sea- 

 level due to return of water which had been congealed on the land; 

 depression of sea-level due to decreasing gravitative attraction of 

 the ice masses; and uplift of the land due to isostatic, or other, 

 readjustment consequent upon removal of ice burden. None of 

 the three can be exactly evaluated from the data now available, 

 and the effect of the third can be estimated only from field evidence. 

 Mathematical calculations will, however, help to crystallize opinion 

 concerning their interaction. 



Woodward's classic contribution 3 to the subject does not exactly 

 meet the situation at hand. His assumptions concerning area and 



1 H. P. Little, "Pleistocene and Post-Pleistocene Geology of Waterville, Maine," 

 abstract of paper presented before the Geological Society of America, December, 1916. 



2 J. Barrell, "Factors in Movements of the Strand Line and Their Results in the 

 Pleistocene and Post-Pleistocene," Am. Jour. Sci. (4), XL (1915), 1-22. 



s R. S. Woodward, "On the Form and Position of the Sea-Level," U.S. Geol. 

 Survey Bull. 48, 1888. 



