25 



some g^eographical feature of the vicinity. Some of these areas are 

 contiguous, and some owe their existence to the same causes. The 

 names, therefore, do not indicate areas which are geologically dis- 

 tinct, but merely general locations in which the field work was prose- 

 cuted. The geography of each of these regions will be described 

 separately. 



The Havana Area. — The Tazewell sheet of the Field Operations 

 of the Bureau of Soils (Bonsteel, igo^a) shows the northern extrem- 

 ity of this deposit, and illustrates its relation to the glacial valley of 

 the Illinois river. North of Pekin, in Tazewell county, the Illinois 

 river cuts through the Shelbyville and Bloomington moraines, flow- 

 ing close to high bluffs on its left (eastern) side. From this point 

 southward the river crosses the broad glacial valley diagonally 

 toward the right, exposing a triangular area of lowland between the 

 channel and the east bluffs. The sand is deposited in this glacial 

 flood-plain. At Pekin the plain is about two miles (3 km.) wide; 

 below that city it widens more abruptly, and near Green Valley is 

 14 miles (22 km.) wide. At some places near the river the plain is 

 covered with modern alluvial deposits, and it is crossed by the Macki- 

 naw river with its broad flood-plain. The remaining area is occupied 

 by sand and by a sandy loam, shown in the Soil Survey as Miami 

 sandy loam. The latter lies at a lower level and represents the original 

 alluvial deposits upon which the sand has been superposed. In this 

 county 22,976 acres (90 sq. km.) are covered with sand. South of 

 Tazewell county the plain retains its maximum width across Mason 

 county, and then becomes gradually narrower toward the south, 

 terminating near Meredosia, Morgan county, with a total length of 

 approximately 75 miles (120 km.). While sand deposits occupy only 

 a portion of this area, their aggregate extent is large and has been 

 estimated (Hart and Gleason, ipoy: 145, 146) at 179,200 acres 

 (700 sq. km.). 



The Chicago, Peoria and St. Louis railway traverses the areas 

 from Peoria through Havana to Virginia, and a good idea of the 

 general topography may be gained from its trains. The exposed 

 areas of Miami sandy loam, which forms the foundation of the whole, 

 are irregular in shape and extremely variable in size, ranging from a 

 few^ acres up to several square miles. They are almost entirely under 

 cultivation. Above them rise the low sand hills (PI. I, Fig. i), usu- 

 ally gently undulating at their margins but, if large in extent, fre- 

 quently quite level toward the center. These vary in size from mere 

 hills of a few acres up to continuous deposits several miles in extent. 

 Their average height is probably 20-30 feet (6-10 m.), but isolated 



