31 



level areas or low ridg'es with a generally east and west direction, and 

 has a total extent, as estimated by the Bureau of Soils, of 25,088 

 acres ( 100 sq. km.). 



This sand differs essentially from the other areas described in its 

 upland position. In some places it forms the bluffs of Sugar river, 

 but in the center of its area it occupies the highest ground between 

 the two river valleys and over 100 feet (30 m.) above them. Its 

 position indicates that it is not of fluviatile or lacustrine origin, as 

 stated in the Soil Survey report. Leverett's account of its origin 

 {i8pp: 131-138) is the most satisfactory, connecting the sand with 

 the invasion of the lowan g^laciers. The western border of the lowan 

 glaciation enters Illinois at the valley of Sugar river, extends south 

 along that river and southwestward along Pecatonica river to the 

 western edge of the county, and thence east to the Rock river. The 

 particular area of sand deposition is thus within the limits of the 

 lowan glaciers, and the sand itself is regarded by Leverett as the drift 

 of the lowan invasion. 



There is no present evidence of the recent existence of extensive 

 prairies in the Winnebago area. Aside from a few deep depressions 

 with a hydrophytic veg'etation, the whole area is either forested or 

 under cultivation. 



CUMATE 



The g'eneral climatic conditions of the northern and central parts 

 of Illinois are shown in the following diagrams, taken from Henry 

 (ipod). Dubuque, Iowa, is located on the Alississippi river just 

 north of the Hanox'er sand area. Beloit, Wisconsin, is situated on 

 the Wisconsin-Illinois state line at the eastern edge of the Winnebago 

 area. Keokuk, Iowa, is on the Mississippi ri\er, near the southern 

 end of the Oquawka area. Spring-field, Illinois, is in the central part 

 of the state, east and southeast of the Havana area. Peoria, Illinois, 

 is on the Illinois river, at the northern end of the Havana area. The 

 first four stations, being located at the extreme edg^es of the general 

 sand areas of the state, will indicate the extremes of climate at the 

 north and south, and the conditions of the intervening reg'ion may be 

 approximated by interpolation. Fig'ure i shows that the seasonal dis- 

 tribution of heat is of the continental type, with moderately cold 

 winters and hot summers, and with occasional great extremes of heat 

 and cold. It may again be mentioned that the official temperatures, 

 taken under a shelter of regular pattern, do not represent the actual 

 temperature to which plants are exposed. This is particularly true of 

 plants growing in exposed sand, where the surface temperature in 



