56. The name.—This level land of fertile soil is called the Prairie Corn and Small Grain Belt, because almost every farmer there grows corn and nearly always one of the small grains also, wheat or oats. Corn is the most important crop of all, partly because the soil and climate suit it so well, and partly because corn yields about twice as maw bushels to the acre there as does wheat. Corn, wheat, and oats are all grown in other regions also (Figs. 56, 72, 90, 93), but no other region grows so much corn as this one.
57. Bounds.—On map, Fig. 21, find what regions bound the Prairie Corn and Small Grain Belt. Which are lower than this region? Which are higher? The western boundary is set by a line where little rain or unsuitable soil stops the good corn crops. (Sec. 104). Its northern boundary is set by a region with a shorter summer, where the growing season is not long enough for corn to ripen, or where the nights are too cool for such a crop. The Great Lakes are so large and deep that their waters stay comparatively cool all summer. Because of the breezes from the cool waters of Lakes Michigan and Erie, the farmers along their shores do not grow much corn, although corn fields thrive a few miles back from the lakes.
58. Climate.—In winter the Prairie Corn and Small Grain Belt is a land of frost and snow, of sleds and skates. In the northern parts the streams and lakes are covered with ice for many weeks each year. In summer the weather is as warm as that of the Cotton Belt, but the season between frosts is not so long. It is too short for cotton, but not too short for corn. Both of these useful plants need a warm, moist summer, but cotton needs seven months while corn can grow in five months.
How does it happen that the Corn Belt and the Cotton Belt have so much rain, while the region to the west has so little? To understand this difference in the weather we need to know about the storms which make the rainfall in this part of the world.
59. The cyclonic storms.—Strangely enough, there is system about these storms. They work according to rules, and usually follow about the same paths. They may start anywhere between southern Texas and Alberta (Figs. 91, 94). But no matter where they start, cyclonic storms in the United States travel from the west, work easterly, and pass off to the northeast. (Fig. 65.) If you should ride above one of these storm areas in an airplane, you would see the wind blowing the tops of trees in the same direc tion that the arrows point. (Fig. 59.) What
direction is that? The wind twists around a center. Is the twist in the direction taken by the hands of the watch? The center of this storm is near Kansas City. The wind blowing toward it from the south crosses Louisiana and Mississippi, and brings moist air from the Gulf of Mexico. The wind blowing toward it from the south west crosses western Texas, and is therefore hot and dry. The wind blowing toward it from the northwest comes from Nebraska and Dakota. It is cool and dry.
60. The rainfall.—Now it so happens that the air blows in toward the center of this storm, and then goes up a mile or two above the ground (Fig. 66). In going up the air becomes cooler. Since cool air will not hold as much moisture as warm air, some of the water is squeezed out of the air and falls as rain. Look at the northwest and southeast quarters of the storm, Fig. 59. What are the wind directions in each? Which quarter has the more water for mak ing rain? Why? Which is warmer? Why? 61.. The cyclone.—These storms are called cyclones because they turn like a wheel or cycle. They twist round and round as they go across the country. These storms are not the same as those popularly called cyclones (Sec. 72). Each one is several hundred miles across. One or two are crossing the United States all the time. They bring the rain to the Cotton Belt and to the Prairie Corn and Small Grain Belt.
62. The movement of the storm.—Figure 60 shows the same storm the next day. It has moved eastward, and is now central east of the Mississippi River.
Look at the place on the Mississippi River that had a southeast wind the first day.
What wind has it the second day? Where does this wind come from? Which of these two days is cooler at this place? Eastern Kan sas and Nebraska had rain the first day. They have clear weather on the second day.
But the places to the south and east of the storm center are receiving winds from the sea, winds that are full of moisture for making rain. The third day (Fig. 61), our storm has passed to the St. Lawrence Valley, and the moist rain wind is blowing across southern New England and Nova Scotia, and the dry clearing wind is blowing across the Great Lakes and the states to the south.