196 Frank Carney 



The Appalachian mountains and bordering Allegheny plateau 

 impeded its progress; consequently, the margin of the ice eastward 

 of the axis of the Mississippi valley had a northward trend. These 

 large physiographic provinces gave the glacier its general outline, 

 while local topography caused the minor irregularities of the mar- 

 gin. Parts of the Alleghenj^ plateau are dissected by north-south 

 valleys. This condition is noted in central and western New 

 York. These valleys produced in the ice-front a very dentate 

 outline. During both the progress and the retreat of the glacier, 

 each valley was occupied by a tongue extending several miles 

 beyond the main ice mass. The plateau parts of Ohio are also 

 irregular in relief. Where its valleys were coincident with the 

 direction of ice motion, tongues and lobes extended into them, 

 and often moved many miles beyond the ice sheet proper. The 

 Grand River valley, the Scioto, and the Miami, each caused a 

 lobation in the ice front. Slighter valleys, contiguous to these, 

 caused minor details along the margin of these lobes. The retreat- 

 al moraines and smaller loops enable us now to decipher the value 

 of this topographic factor in reconstructing the outline of the 

 ice-front. 



Glacial deposits in valleys. Valleys contiguous to the ice front 

 always carried a great supply of water. If the valley sloped away 

 from the ice, this water flowed off. If the valley sloped towards 

 the ice, the water gathered, forming a lake which continued to 

 deepen till an overflow somewhere about the border of the valley 

 was discovered. Under the former condition, the valleys now 

 usually bear heavy deposits of out wash material, which has been 

 progressively terraced during and since glacial times. 



When a speedy retreat followed a stationary position, main- 

 tained a long time by the ice, morainic terraces were left along the 

 valley slopes. Where, on account of minor irregularities in the 

 valley wall, local bodies of water gathered, the drift accumulat- 

 ing in them was prevailingly washed and stratified. When gravel 

 and sand prevail in these deposits they are called '' kame terraces." 



If, in a valley, the ice became less active and some portion of it 

 was left stagnant, later stream deposits might completely burj^ all 

 or part of it ; such a buried block of ice would melt slowly ; possibly 

 hundreds of years elapsed before all had disappeared. The posi- 

 tion of a detached mass of ice is to-day indicated by a basin called 

 a "kettle hole;" when containing water, a "kettle lake." Modified 

 drift, and, less frequently, kettle lakes, characterize kame areas. 



