668 H. L. ALLING GLACIAL LAKES OF CENTRAL ADIRONDACK^ 



ELIZABETHTOWN GROUP 



Commencing somewhat later in time, a series of events occurred in the 

 Elizabethtown Valley similar to those which took place in Keene Valley. 

 When better known, the history of this. succession of lakes promises to be 

 just as dramatic and interesting as that of the other series, for a glacial 

 lake origin is now assigned to many of the terraces that geologists for- 

 merly attributed to the temporary holding back of drainage waters by 

 moraines. Apparently the Elizabethtown group of lakes succeeded each 

 other with such rapidity that they passed out of existence by the time the 

 latter stages of the Saranac Waters drained through the Black Mountain 

 channels. It is probable that the Wilmington Lake discharged through 

 the Copperas Pond channel directly into the marine waters. 



Post-Lacustrine Deformation 

 general discussion 



It has been pointed out that at the maximum extent of the Wisconsin 

 ice-body the load on the land surface must have been tremendous. This 

 weight compressed the land below its former level, which consequently 

 rose when the load was removed by the retreat of the glacier. As these 

 glacial lakes existed during the waning of the ice-sheet, the succession of 

 terraces, deltas, and beaches form today a series with altitudes slightly 

 rising to the north. The measurement of the amount of deformation has 

 been attempted for a number of the different lake levels. The work of 

 Professors Woodworth and Fairchild in the Connecticut and the Cham- 

 plain-Hudson valleys has greatly cleared up our conceptions regarding 

 Pleistocene submergence and postglacial deformation. 



At the same time there exists some uncertainty as to the character of 

 the uplift. (1) Was the upward movement gradual and uniform or (2) 

 was it in the nature of a wave or a series of sudden uplifts? I believe 

 that the problem will be greatly clarified by accurate measurements of 

 beaches, deltas, etcetera, situated at higher levels to supplement those 

 mapped at lower altitudes. The shore phenomena of the lakes above de- 

 scribed afford a splendid opportunity to determine the amount of defor- 

 mation of the land surface, for they give us a series of datum planes 

 higher than those in the Champlain Valley, which was occupied by ice 

 during the entire period that covered the existence of the various lakes 

 above described. 



A glance at the table given below would indicate that the uplift fol- 

 lowed very soon after the retreat of the ice and was a uniform and gradual 

 process during the time represented by the lakes. 



