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completed. The range of elevation four hundred ninety to five hundred 
thirty equals forty feet over large areas with places of forty-five feet or more. 
A cross profile from bluff to bluff shows these ridge tops to be the highest 
points between bluffs. Water covering these ridges must have covered 
the valley from side to side making a stream of from five to six miles wide 
and forty to fifty feet deep. Just how much of the year or for how long 
periods the water maintained such a volume it would seem impossible to 
say, but probably the maximum volume was reached in summer and main- 
tained through the summer months, declining. as winter came on. The 
assumption is that the largest volume of water was produced by the summer 
melting of the Great Ice Sheet that formerly overspread the Northern 
United States and much of Canada. Whether the west deeper side of the 
valley was then lower than the terrace portion cannot be stated certainly, 
deeper water probably covered the part of the valley that now shows the 
greatest depth. A depth of twenty feet of water is shown for the highest 
parts of the site of Terre Haute. 
