GLACIAL WATERS IN THE LAKE ERIE BASIN 9 



Hamburg, north and east, the land surface is more dissected by 

 streams and the general slope is more gradual. In consequence 

 of these characters the glacial stream and lake phenomena are 

 distributed over a wider belt and more irregularly. 



With reference to both ancient and modern drainage there are 

 two sets of base levels. The lowest is the present water surface 

 of Lake Erie, taken as 572 feet over ocean. The other baselevel 

 is the series of ancient and higher waterlevels of the great glacial 

 lakes Whittlesey and Warren. These old high-level beaches are 

 spread through a vertical space of about 70 feet, and lie just below 

 the foot of the steepest land slope. 



The ancient shore lines are no longer horizontal, but have suf- 

 fered along with the land surface on which they lie a tilting or 

 differential uplift, so that they now rise toward the northeast at 

 the rate of nearly 2 feet a mile [see p. 77]. 



OUTLINE OF GLACIAL HISTORY: THEORETIC PROBLEM 



It will help the reader to a clear mental grasp of the subject 

 if the broad features in the topography and the main events in the 

 geologic story can be clearly appreciated apart from details. 



There are four distinct elements in this study, (i) The general 

 topography or the broader configuration of the land surface. 

 (2) The location and trend of the front of the glacier, which is the 

 variable factor. (3) The flow of the escaping waters, or the stream 

 phenomena, which changed along with (2). (4) The position 

 and the effects of the lake waters which followed the retreating 

 ice front. We will discuss these briefly in order. 



(i) The general topography has already been described as a 

 broad valley or basin extending northeast by southwest. The 

 present Lake Erie has no part nor significance in this history, it 

 being only the successor of the ancient glacial lakes, and giving 

 its name to the basin, and marking the lowest part. The Lake 

 Erie basin should be recognized as continuing northeastward 

 beyond the lake, and as blending with the Ontario basin. The 

 southern slope of this general basin, facing northwest, and extend- 

 ing from the Pennsylvania boundary northeastward to Batavia, 

 is the stage on which our glacial drama was enacted. 



(2) The geologic events which we are studying belong to the time 

 when the last ice sheet of the glacial period was disappearing from 

 the region. At an earlier time, when the great ice body was at its 

 maximum, it had covered, practically, all of New York State, and 

 the movement of the ice mass had been toward the southwest, 



