258 THE ICE AGE IN NORTH AMERICA. 



370 feet, and in another, 530 feet of till was penetrated, and 

 the well abandoned before rock was reached. In Dayton, 

 Montgomery county, the glacial deposit was found to be 247 

 feet; in Cridersville, Aaglaize county, 300 feet; in New- 

 ark, Licking county, 235 feet ; in Lebanon, Warren county, 

 256 feet ; in Osborn, Greene county, 207 feet ; in Hamilton, 

 Butler county, 214 feet. These are all, perhaps, in pre- 

 glacial valleys. But the average in various counties is cer- 

 tainly significant. In Auglaize county, six borings give an 

 average of 141 feet; in Butler county, four borings, 116 

 feet. 



With reference to the correctness of this representation, 

 it should be remarked that borings prosecuted in this man- 

 ner are more likely to give an underestimate than an over- 

 estimate of the real facts ; for, as is well known, it is much 

 easier and less expensive to drill through the sedimentary 

 rocks than through deep deposits of till and looser drift ; 

 so that the aim of the prospectors is to begin their wells at 

 points where the rock will be reached at as small a depth as 

 possible. But so completely have the pre-glacial lines of 

 erosion been obliterated in many places in Ohio, that it is 

 impossible to calculate the proximity of the rock to the sur- 

 face. Where the deepest drift was penetrated (530 feet in 

 Champaign county), special effort was made to locate the 

 boring where the superficial deposits were shallow ; but, as 

 the result proved, the surface indications were deceptive and 

 a serious mistake was made, involving the contractor in great 

 loss. It should, however, be observed* that the deep well 

 at St. Paris lies in the line of one of the great terminal 

 moraines traced by Mr. Leverett across central Ohio, and 

 where the depth of the glacial deposits is supposed to be 

 excessive even in a moraine. 



Mr. Upham estimates the mantle of drift that conceals 

 the rocks in central Miunesota to be between 100 and 200 

 feet deep. In the Eed River region, to the north, and over 

 a wide belt stretching many hundred miles along the flanks 

 if the Rocky Mountains, in the Dominion of Canada, the' 



