402 FIRST TEAR SCIENCE 



These plains are very fertile and are usually called 

 " bottom lands " by the farmers. They are often unhealthy 

 because of floods and poor drainage. Where the water in 

 the river rises rapidly and to a considerable height, it is 

 dangerous to inhabit these plains. Thus it is necessary 

 to build strong levees along the river bank, as in the case 

 of the lower Mississippi and some of its tributaries. But 



" BOTTOM LANDS." 



sometimes these plains are so fertile that they are densely 

 populated, as the plain of the Ganges. 



186. 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 emigrant did not need to go to the trouble and 

 delay of clearing the forests before beginning to farm. 

 Cultivation could begin in earnest with the first spring, 



