76 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



3. Appalachian Mountains and Allegheny Plateau. The soils 

 of the eastern ranges of these mountains are of igneous or 

 metamorphic origin, while the western ranges and the Allegheny 

 plateau are of sedimentary origin. General farming is not 

 practiced in a large part of this area on account of the unevenness 

 of its topography. The land is, however, well suited to grazing 

 and fruit growing. 



4. Limestone Valleys and Uplands. These occur in narrow 

 valleys among the Appalachian mountains and plateaus near by, 

 and in two large areas, one in central Kentucky and Tennessee, 

 the other in Missouri and northern Arkansas. The limestone 

 soils are derived from the weathering of limestone, and many of 

 them contain but a small percentage of the original limestone 

 rock. Each foot of the soil is the residue from the weathering 

 of many feet of the rock. 



5. Glacial and Loessial Deposits. This area covers a large 

 portion of the United States, especially in the north-central 

 states. A large portion of this area was covered by a great con- 

 tinental glacier, which in its southern movement filled up valleys, 

 plowed off hills and mountains, and deposited the ground-up 

 material varying from a few feet to over 30 feet in thickness. 

 The soils are partly till, or heavy clay compacted under the 

 glacier, but largely "loess," a fine silty deposit containing lime- 

 stone and very fertile. Some of the material was brought long 

 distances, but most of it is composed of ground-up underlying 

 rock largely deposited from glacial streams. 



6. Glacial Lake and River Terraces. These are deposits 

 formed by the Great Lakes, after the close of the glacial period, 

 when they were much larger than they are now. Several terraces 

 marked by the old shore line can be observed. The soils vary from 

 beach gravels to off-shore deposits of heavy clays, and the 

 material worked over by the water is partly of sedimentary and 

 partly of igneous origin. 



7. River Flood Plains. These soils are most extensive along 

 the Mississippi and its tributaries, and along rivers in Texas and 

 Louisiana, though soils of this group are found in all areas. The 



