THE DRIFT-DEPOSITS OF THE NORTHWEST. 293 



gether by reason of the westward attenuation, and finally the entire 

 disappearance of the salina formation in which it is largely excavated. 

 The ice was then thrust up on to harder rocks that form the basis of 

 Northwestern Ohio and Northeastern Indiana. Lake Michigan was 

 terminated southwardly by the eastward trend of the rocky outcrops 

 at an angle that the ice could not follow. The Red-River flats of Min- 

 nesota correspond to the Winnipeg basin in the same way that the 

 Black-Swamp district of Ohio does to the Lake-Erie basin, or the 

 prairie district surrounding the southern end of Lake Michigan does 

 to the basin of that lake. 



It must be remembered, however, that throughout the continuance 

 of the ice-period the motion of the ice brought it finally into a climate 

 where it could not exist as ice. It gave rise to countless streams of 

 water. The broad, level country of the Northwest was not sufficiently 

 irregular to gather the ice, and consequently not the water, into val- 

 leys having a north-south direction. The water from the ice acted all 

 along the ice-foot with a comparatively uniform energy. If it was ul- 

 timately gathered into large streams, it must have been at considerable 

 distances from the glacial field. It must be remembered also that the 

 accumulated precipitation of the entire year over broad, continental 

 areas was preserved from thaw till it arrived at the latitude of the 

 limitation of the glacier, and there its full volume was discharged. It 

 was as if the entire precipitation of the continent say from the lati- 

 tude of Chicago to the north-pole were concentrated on a belt of ter- 

 ritory, say of fifty miles in width, running east and west across the 

 continent, and having the direction of the marginal line of the ice- 

 foot. Thus a constant sheet of turbid, running water would act on all 

 objects over which the ice-foot retreated. 



We must not forget, in recalling to our imagination the scenes and 

 events of the ice-period, to inquire what were the position and the con- 

 dition of the drift to which it gave origin. 



In regions far to the north, the eye probably would not be able to 

 discern any object except that of the universal ice. The surface of 

 the ground would be thousands of feet below the traveller, if we may 

 be permitted to presume so hardy a human being. Like Dr. Kane ex- 

 ploring the great Humboldt Glacier of Greenland, he would meet with 

 countless obstacles and dangers. But those obstacles would consist 

 of hummocky ice, or crevassed ice, or perpendicular ice-walls. He 

 would see no soil, no rocks, no vegetation, no animal life. The winds 

 would whistle, storms would rage, snow would be drifted about, and 

 the ineffectual sun would rarely venture to smile on the dreary waste. 

 Farther to the south, the explorer would find isolated spots of bare 

 ground. He would see about them the accumulated debris of bowl- 

 ders, gravel, and dust, from constant winds, spread more or less over 

 the ice-field, staining its painful whiteness, and showing the more grate- 

 ful aspect of earth and stones. Another hundred miles farther south, 



