IO 



NEW YORK STATE MUSEUM 



following the axis of the Erie basin. But at the time we are con- 

 sidering the ice sheet had long passed its maximum stage, and the 

 front had receded, due to the excess of melting at the margin over 

 the supply by flow from the northward. There now lingered over 

 the Erie basin a great mass or lobe of the continental glacier which, 

 since it was no longer subject to great pressure or push from the ice 

 mass on the north, was reposing in the basin as a comparatively 

 stagnant mass. It was not a rigid, inflexible body, like a small 

 block of ice in the summer sunshine, but its great bulk and weight 

 gave it a practical plasticity and a slow spreading movement, like a 

 block of pitch or asphalt in the summer heat. This spreading flow 

 was naturally radial or outward from the center, and consequently 

 the direction of flow of the Erie ice mass over our district was from 

 the northwest. The margin of the ice was at right angles or normal 

 to the direction of flow, and hence extended northeast by southwest 

 along the northwest-facing land slope. As the recession of the ice 

 front was very slow it reposed for ages (we have no way of measuring 

 the time) against the steeper part of the valley slope, and its 

 position there, slowly falling or backing away, is indicated by the 

 lines of rock rubbish or moraine drift dumped at the ice margin, 

 and by the stream channels cut by the drainage past the ice front. 

 Other belts of moraine farther landward mark earlier pauses in the 

 ice retreat [see fig. i, p. 12]. 



(3) The drainage. If the reader now apprehends the relation 

 of the ice body to the general land surface (a huge ice mass filling 

 the bottom of the Erie valley and resting against the northwest- 

 facing land slope with its margin extending along the horizontal 

 contours of that slope) he will appreciate the fact that the stream 

 flow of that time must have been very unlike the present. On the 

 higher, exposed land surface the streams must have flowed down 

 the slopes (northwestward) as they do today. But the ice front 

 opposed their course and they could pass neither through, over, 

 nor beneath the glacier; they could flow only alongside or past 

 the ice margin. This land drainage along the ice border was 

 augmented by the abundant water derived from the melting of the 

 ice body itself. 



The question will now arise as to the direction of escape for the 

 waters, whether to the eastward or westward. It has been found 

 that the eastward escape was impossible, not only because the 

 neighboring land is higher in that direction, but for the reason that 

 at this stage in the glacial retreat the Ontarian ice lobe was pressing 

 against the high ground in central New York. The escape was 



