210 MAN AND THE GLACIAL PERIOD. 



we will go back to finish the history of the preglacial 

 channel around the Falls of St. Anthony. As early as 

 the year 1876 Professor N. H. Winch ell had collected suf- 

 ficient evidence from wells, one of which had been sunk 

 to a depth of one hundred and seventy-five feet, to show 

 that the preglacial course of the stream corresponding to 

 the present Mississippi River ran to the west of Minne- 

 apolis and of the Falls of Minnehaha, and joined the main 

 valley some distance above Fort Snelling, as shown in the 

 accompanying map. 



This condition of things was at one time very pain- 

 fully brought to the notice of the citizens of Minneapolis. 

 A large part of the wealth of the city at that time con- 

 sisted of the commercial value of the water-power fur- 

 nished by the Falls of St. Anthony. To facilitate the 

 discharge of the waste water from their wheels, some mill- 

 owners dug a tunnel through the soft sandstone underlying 

 the limestone strata over which the river falls ; but it very 

 scon became apparent that the erosion was proceeding 

 with such rapidity that in a few years the recession of 

 the falls would be carried back to the preglacial channel, 

 when the river would soon scour out the channel and de- 

 stroy their present source of wealth. The citizens rallied 

 to protect their property, and spent altogether as much 

 as half a million dollars in filling up the holes that had 

 been thoughtlessly made ; but so serious was the task that 

 they were finally compelled to appeal for aid to the United 

 States Government. Permanent protection was provided 

 by running a tunnel, some ways back from the falls, com- 

 pletely across the channel, through the soft sandstone un- 

 derlying the limestone, and filling this up with cement 

 hard enough and compact enough to prevent the further 

 percolation of the water from above. 



