GLACIAL WATERS IN BLACK AND MOHAWK VALLEYS 4I 



and the correlating outlets can be nowhere except through the 

 Delanson hollow and on the face of the Helderberg scarp, where 

 the ice-compelled rivers have left their unmistakable tracks. At 

 Lee Center, northwest of Rome, and eastward are sluggish-flow 

 channels at declining levels, made along the stagnant ice margin, 

 while the lake levels were controlled by the ice front on the Rotter- 

 dam salient. 



From localities of known position for the ice margin the latter 

 can be extended theoretically, lapping on the land at levels slowly 

 rising northward and falling southward. 



Between known positions of the ice at different periods the loca- 

 tion for time intermediate can be approximately interpolated. 



The maps (plates 9-17) are an attempt to portray several stages 

 in the recession of the latest ice sheet. A continuous waning of the 

 glacial lobes is suggested by the maps. However, the ice sheet did 

 not pass away by continuous and steady recession but by oscillations, 

 readvances and reretreats ; and some of the readvances may have 

 covered considerable territory and have seriously changed the 

 drainage. At present our knowledge of these elusive changes in the 

 glaciers in the Mohawk-Hudson region is almost nothing and no 

 account can be taken of them. 



The maps make no claim to accuracy, except at a few points for a 

 few stages in the history. They are only suggestive and intended 

 to give in a graphic way the broad facts in the general history. The 

 positions of the ice limits as indicated in the maps are separated by 

 long periods of time, perhaps in some cases thousands of years, 

 during whi(!h oscillations of large extent may have occurred. The 

 positions of the ice fronts at both ends of the Mohawk valley are 

 definite for the phases shown in plates 14-16. 



These maps are an extension and correction of plates 34-42 of 

 the preceding paper (N. Y. State Museum Bulletin 127) on Central 

 New York drainage. 



Between the stages depicted in plates 16 and 17 is a very long 

 interval unmapped. During this time central New York had a 

 varied lake history, including at least the Second Vanuxem, Warren 

 and Hyper-Iroquois waters. If the ice in the Hudson advanced in 

 sympathy with that in the Syracuse district it may have again 

 blocked the Mohawk valley. But with the beginning of Lake 

 Albany we have no means, now recognized, of comparing the limits 

 of the ice in the Hudson valley with those in the Ontario. Rather 

 than depict stages between those of plates 16 and 17 in a purely 



