108 
to the bottom-lands, of which about 17 square miles have been 
cleared of the forests and placed under cultivation, 7 represent 
river and lakes at low-water stage, 10 are permanent marshes, 
and the remaining 22.5 are covered by forests, and lie at so low 
a level as to be subject to frequent overflow. It is difficult to 
distinguish between marsh and woodland in those areas 
covered by low growths of willow (Salix nigra) or sparsely 
wooded with willow-trees of considerable size. As their low 
elevation renders them subject to overflow on slight rises of 
the river, and as the vegetation is usually of a semiaquatic 
nature they are on our map in large part included in areas 
designated as marsh. As the elevation increases, maples 
(Acer dasycarpum) appear among the willows, then the green 
ashes (Fraxinus viridis), while in the higher bottoms the elms 
(Ulmus americana) form the major part of the forest, with 
maples, box-elders (Negundo aceroides), sycamore (Platanus occi- 
dentalis), pecans (Carya oliveformis), oaks (Quercus palustris), and 
clusters of cottonwoods (Populus monilifera) interspersed. The 
marshes and lagoons, especially along the lower part of the 
river, are often fringed with dense and impassable thickets 
of button-bush (Cephalanthus occidentalis) and buckbrush (For- 
esteria acuminata). 
Cooley (’91) gives the average height of the banks of the 
Ihnois above low-water level as 10 feet for the region between 
Copperas Creek and Havana and 11 feet from Havana to the 
mouth of the Sangamon River. The range in height for the 
same distance is 7 to 12 and 9 to 12 feet respectively. The 
greater height below Havana is doubtless due to tke deposits 
contributed by Spoon River. The dam at La Grange, com- 
pleted October 10, 1889, has raised the water about two feet at 
Havana, so that the actual height of the banks above the water 
at its lowest stage, under present conditions, averages less than 
8 feet. The immediate banks are usually higher than the ad- 
jacent bottom-lands. This is true of the tributary streams also, 
and is especially well marked in the case of Spoon River, 
which carries large amounts of sediment at times of flood. It 
