38 FARM DEVELOPMENT 



period of melting and recession of the yet moving south 

 edge of the glacier, was added to the annual rainfall and 

 greatly enlarged the streams flowing into the Mississippi 

 river, and the drainage of this whole region was very 

 different from what we see at present. Now only a part 

 of the annual rainfall must find its way to the Gulf of 

 Mexico. This excess of water during the recession of the 

 glacier is illustrated by a spring rain melting the snow, 

 combining the rain and the snow water into a flood. 

 The front edge of the glacier, instead of being a straight 

 line, was very irregular. Great streams, or fingers, of 

 ice flowed south through the valleys and lower areas, in 

 advance of the general body of the glacier. The reces- 

 sion was sufficiently rapid, in spite of the slow forward 

 movement of the frozen water, so that the ice which 

 flowed to a given point, and there melted, added an 

 immense amount of water to the usual rainfall. All 

 this water swelled the streams in the midsummer so 

 that, instead of the small streams winding through the 

 flats in our valleys, there were rushing torrents rising 

 nearly to the tops of the present bluffs, which were then 

 banks of the large streams. 



Many neighborhoods in the states mentioned have 

 very interesting illustrations of how the glacier and the 

 large volume of water from the melting glacier operated 

 in modifying the land surface. Every citizen of such 

 regions should study the glacial geology so as to be able, 

 by observation, to understand the phenomena presented 

 by the surface features in his own neighborhood. 



Glacial drift or till. Prior to the time of the glacier 

 there was loose soil, rock, sand, clay, etc., covering the 

 underlying rocks of the region over which the glacier 

 flowed. The ice, in flowing over this surface, gathered 

 up much of the loose clay, sand and stones, and also tore 

 loose and ground up more of the underlying rocks. This 

 whole mass was made finer by the immense forces in 



