124 SCIENCE AND SOIL 



directly from till or loess. The soils formed from the till are confined to that 

 part of the country lying north of the southern limit of glacial action, but the 

 loess soils occur also south of this line, especially along the Mississippi and 

 Ohio rivers and in Kansas and Nebraska. The line of the southern extension of 

 the ice sheet touches the Atlantic coast about New York City, passes through 

 northern New Jersey, southern New York, and northwestern Pennsylvania, 

 swings southward through Ohio to Cincinnati, crosses the Mississippi River 

 at St. Louis, and follows the south side of the Missouri River into Montana, 

 where it crosses the Canadian boundary line, then dips southward into Idaho 

 as a long lobe in the mountainous nonagricultural region, and crosses the 

 northwestern part of Washington, including the Puget Sound region. 



Practically all of the United States north of this line was covered in recent 

 geological time by a great continental glacier, many hundreds, and even thou- 

 sands, of feet in thickness. This great ice sheet, moving in a southern direction, 

 filled up valleys, planed off the tops of hills and mountains, ground up the 

 underlying rocks, carried the derived material both within and upon the ice, 

 and finally deposited the gravel, sand, silt, and clay, as a mantle, varying in 

 thickness from a few feet to more than 300 feet. Often this material has been 

 transported hundreds of miles, and is wholly unrelated to the underlying rocks, 

 but in some places the movement has been slight, and the drift consists very 

 largely of the ground-up underlying rock. Over a large porportion of the 

 area covered by the drift and also along the Ohio and Mississippi rivers and 

 in Kansas and Nebraska, the surface material consists of a fine silty deposit, 

 known geologically as "loess" and "Plains marl." In the classification of the 

 glacial soils, three important series Miami, Marshall, and Volusia having 

 distinct characteristics have been recognized and, in addition, quite a number 

 of miscellaneous soils which cannot be put in any series. 



Marshall series. Dark -colored upland prairie soils. The principal soils 

 of the great corn belt belong to this series, while in the Northwest the finest 

 wheat soils are found in this group. They are among the best general farming 

 soils of the entire country. 



Miami series. Light-colored upland timbered soils. The different mem- 

 bers of this series are considered good general farming soils and have in ad- 

 dition special adaptations for truck, fruit, small fruit, and alfalfa. 



Volusia series. Light-colored soils with yellowish sut soils, derived by feeble 

 glacial action from sandstones and shales. The soils of this series are adapted 

 to the production of potatoes, grass, oats, buckwheat, and, in the less elevated 

 positions, to corn. 



GLACIAL LAKE AND RIVER TERRACES 



Another important group of soils occurs in the glacial region, principally 

 as terraces around lakes, or along streams, or as deposits in areas which were 

 formerly covered by water. At the close of the glacial epoch the lakes in this 

 part of the United States were not only more numerous, but the waters of those 

 which remain reached a higher level and covered areas that are now far above 



