CHAPTEK XXVI. 



EVIDENCES AND THEORIES OF AN ICE AGE. 



There is abundant and unassailable evidence 

 that at one time, ages ago, a vast ice sheet cov- 

 ered the whole of the northern part of North 

 America, extending south in Illinois to a point 

 between latitudes 37 and 38. This is the most 

 southerly point to which the ice sheet reached. 

 From this point the line of extreme flow runs 

 off in a northeasterly and northwesterly direc- 

 tion. The northeasterly line is through south- 

 eastern Ohio and Pennsylvania, striking the 

 Atlantic Ocean about at New York, thence 

 through Long Island and up the coast of 

 Massachusetts. Northwesterly it follows the 

 Mississippi River to its junction with the Mis- 

 souri, which it crosses at a point some miles 

 west of this junction, following the general 

 course of this river a little south of it through 

 the States of Missouri, Nebraska, Dakota, and 

 Montana. The lines, especially the northeast- 

 erly one, are very irregular, shooting out into 

 curves and then receding. This line of ex- 

 treme ice flow is marked by glacial drift so 

 prominently that no one who has studied gla- 

 cial action can doubt for a moment what was 



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