83. Limestone plains.—In the midst of the Ohio Valley are two nearly level plains, with land so rich that the districts are famous for agriculture. The rock beneath the soil of these plains is limestone. We saw in the Black Belt of Alabama and the Black Land of Texas, that limestone forms a fertile soil when it decays. These plains, each several thousand square miles in extent, are the Nashville Basin and the Kentucky Blue Grass Region. Nashville is the center of the Nashville Basin; Lexington is the center of the Blue Grass District. If trees are not allowed to shade the ground, the Blue Grass Region becomes covered with a tough, thick turf of a bluish-green grass, which is excellent for pasture. For many years this limestone plain was famous as the place where the finest carriage and race horses in the United States were raised. The automobile has hurt this business; consequently, the beau tiful horses are now seen in only a few places, and the rest of the Blue Grass Region raises splendid crops of wheat, corn, tobacco, and hemp. Hemp is a plant from whose big stalk the fibers are taken to make cheap rope.
The limestone plains of Kentucky and ' Tennessee, and also some of the hilly sections of the Ohio Valley have many thousands of acres of tobacco, making this re gion the leading tobacco section in the United States, and the city of Louisville the greatest to bacco market in the world. Each year tobacco buyers from many parts of the United States and Europe come here to buy supplies. Tobacco is a crop need ing much labor of the kind that boys, girls, and women can do. Many of the boys and girls who help grow tobacco do not go to school very much. The tobacco plant takes so much plant food that it leaves the soil poor. The grower usually waits several years before growing tobacco a second time on the same field, and even then it must be heavily fertilized.
The rocks beneath these two limestone regions, as in other limestone regions, are honeycombed with caves. (Fig. 19.) One of these is the famous Mammoth Cave, in Kentucky, a wonder of nature which many tourists go to see. In this cave people can go boating on the stream that helped to carry away the limestone and make the cave.
84. Flood plains.—Along the Ohio River and its branches in Kentucky, Indiana, and Illinois, wide areas of lowland are covered from time to time by muddy flood-waters from the overflowing rivers. Then people go about in boats in the woods and fields for miles and miles. These floods sometimes raise the river-level as much as fifty feet at Cincinnati. When the water goes down, it leaves on the flooded land a layer of mud rich enough to fertilize many heavy crops of corn, so that corn is grown there year after year (Sec. 587). Sometimes an occasional summer or autumn flood spoils the crop, but this happens so rarely that these cornlands of the flood-plains are very valuable.
85. Transportation and region of the United States, except the plain along the Atlantic Coast, has rivers so well placed for good boat service. Make a sketch map of this district, marking the navigable rivers (Fig. 80) with double lines. The Ohio has been an important highway since the days of the first settlement of the country west of the Appalachians. Kentucky was the first state west of the mountains, and the first large settlements there were close to the Ohio, because its waters were the great highway.
All the trade that the settlers had was by means of the flatboats that took produce down the Ohio, but which could not be -- brought back again (Sec. 9). Much work has been done to remove rocks and deepen the channel, and many steamboats and barges now carry freight up and down the Ohio very cheaply. Cincinnati and Louisville, the great cities of the Ohio Valley Region, are on the banks of this stream. Both have a large wholesale trade with the small towns and the country stores, and each also has many factories, meat-packing plants, ma chine shops, and iron works.
Cincinnati has also fine potteries and tan neries. The other cities of the Ohio Valley Region are smaller than the two great river ports. Nashville is the capital of Tennessee; Lexington is a horse market; and Evansville is a great market for hardwood lumber, some of which is brought on rafts and steamboats from the forested hills of Kentucky and from the Appalachian Plateau. Wheeling, Charles ton, and Huntington, West Virginia, in the upper part of this district, are among the many towns which manufacture iron, steel, and glass. The coal mines of southeastern Ohio, and West Virginia natural gas help the growth of manufacturing in this section.
86. Resources for manufacturing.—The Ohio Valley has unusual resources for manu facturing. Coal is at hand in West Virginia, Pennsylvania, Ohio, and Indiana. Iron, lumber, and cotton are near. With all of these advantages, manufacturing is increas ing, but it has increased a little less rapidly here than in the northeastern part of the country. Do you think that the reason why manufacturing has not increased as rapidly in the Cotton Belt and in the Ohio Valley as in some other sections is because the summer, so good for crops, is longer and hotter than it is in some other regions? 87. A possible new agriculture.—We need more food from the Ohio Valley if our in creasing number of people are to get the greatest food benefit from the fine produc tive climate and the rich soil of this region. We must learn how to cultivate the hills without letting the soil wash away from them. There are few parts of the United States in which a new agriculture, namely a tree-crop agriculture, is more needed or easier to start than in the Ohio Valley. Nature has done much to show man the way. On many fields which have been cultivated in corn and tobacco until they are abandoned as " throwed-out fields", wild persimmon trees have grown up, bearing heavy crops of fruit that falls in autumn. Sheep and pigs make paths in these fields as they follow a regular route from tree to tree, eating the nourishing fruit. To these trees the hunter, too, goes at night, in order to catch the prowling fat opossum as he eats hilsupper of persimmons.
In this Ohio Valley, wild persimmons, hick ory nuts, acorns, and walnuts have fed many hogs since white men came. These wild products, called ' mast", fed many wild animals in the time of the Indians and before. Wild pecan trees, four feet through the trunk, and bearing delicious nuts, grow along the Ohio and its tributaries. Nature invites man to take these trees, improve them (Sec. 51), and use them as a start in a rich, new tree-crop agriculture which will hold the soil (Sec. 82), make food for animals and food for men, and finally will yield valuable wood and logs.
Experiments here and there show that this kind of tree farming may be very productive. (Secs. 455, 559, 560.) If we keep on with our schools and our scientific agriculture, the Ohio Valley hills should surely have grassy slopes covered with orchards of apple, wal nut, hickory, oak, persimmon, cherry, mul berry, honey locust, and other fruiting trees. The cherries can be dried and canned. The mulberries will be eaten eagerly by pigs and chickens; the acorns by the pigs and sheep. Cattle will eat honey-locust beans instead of corn. The persimmon has long been a very important source of food in China, and is already to be found in American markets. Many other kinds of trees now unused, in this country and in other countries may be made profitably fruitful if given the same degree of scientific care as has been given to change the apple, the orange, and the walnut from unpromising wild trees to the splendid varieties we now have.
These trees can grow on pastured hills, while the level lands in valley and on hilltop can have an intensive agriculture yielding corn, oats, hay, and other crops for which the earth must be plowed.