

PRAIRIES OF THE UNITED STATES 301 



It extended over the eastern part of North Dakota and about 

 half of the province of Manitoba. The slope of the land is 

 here toward the north. As the ice retreated northward it 

 formed a barrier to the drainage and dammed back a great 

 sheet of water in front of it. When the ice melted, the lake 

 was drained, leaving the flat fertile plain through which the 

 Red River of the North now flows. Glacial lake plains 

 of this kind form fertile areas of great agricultural value. 

 The North Dakota-Manitoba area is now one of the most 

 productive wheat regions in the world. 



Prairies of the United States. North of the Ohio 

 River and extending westward beyond the Mississippi is a 

 region of rolling land with a deep, rich soil. Early in the 

 last century it began to be rapidly populated on account 

 of its great agricultural advantages. Owing partly to the 

 fineness of the soil, but mostly to the frequent burning over 

 of the region by the Indians, the area was destitute of trees 

 except in some places along the river courses. 



Thus the immigrant did not need to go to the trouble and 

 delay of clearing the forests before beginning to farm. Culti- 

 vation could begin in earnest with the first spring, and, 

 as a rule, rich harvests could be obtained. The soil here 

 is transported soil ; it is deep and unlike that of the under- 

 lying rock. In some places it is rather stony and in others 

 very fine and without stones. It is so deep that the under- 

 lying local rock is seen only in deep cuts. 



This soil was probably deposited by the great conti- 

 nental glaciers which once covered the region and was 

 spread out either by the action of the slowly moving ice 

 or by the water from the melting ice. This water flowed 

 over the surface in shallow, debris-laden streams, bearing 



