TREE GROWTH IN VICINITY OF GRINNElvL, IOWA 101 



River it may be a mile wide ; and it disappears on the smaller streams 

 only where they become intermittent bearers of surface drainage. It 

 consists of miscellaneous washings from higher ground, enriched by 

 humus and humic substances. 



Only the Miami and Kaskaskia soils were originally timbered. The 

 Kaskaskia loam was often heavily timbered in the more protected river 

 bottoms. These differences in soil are both cause and effect of the 

 characteristic vegetation of the soil areas. 



The following descriptions of these soils as they occur in Tama 

 County, next north of Poweshiek, apply precisely to the region under 

 discussion. The Marshall silt loam "was originally covered with prairie 

 grass, and its present dark color is due to the organic matter which has 

 been incorporated in the soil. . . . The difference between this type 

 of soil and the Miami silt loam is largely one of organic matter, and 

 this has been brought about by the difference in topography and in 

 native vegetation" (p. 12). ^ 



The Miami silt loam "was originally timbered with oak, hickory, elm, 

 maple, and hazel brush. . . . The Miami silt loam occupies the most 

 hilly land in the county" (p. 14). 



"The Kaskaskia loam is an alluvial deposit left on the bottoms when 

 the streams overflowed, added to, to some extent, near the hills and on 

 the smaller streams, by wash from the surrounding types. As these 

 bottoms were once timbered and were more or less damp, the organic 

 matter was not completely removed by decomposition processes, but 

 accumulated from year to year, which accounts for their present dark 

 color" (p. 17). 



"The Marshall loam, to a depth of 10 to 14 inches, is a rather heavy 

 brown loam, similar in color to the Marshall silt loam, but differing 

 from it in containing considerably more fine sand. . . . The type is 

 always found in small, scattered areas, ranging from 5 acres up to half 

 a square mile in extent, and naturally well drained. It is the only soil 

 in Tama County formed directly from the glacial drift, and is devel- 

 oped in places where the loess was deposited as a very thin layer, or 

 where it has been washed away" (pp. 19-20). 



TIMBER ON THE MIAMI SILT LOAM 



The natural timber may be discussed, therefore, as it occurs on the 

 Miami silt loam and on the Kaskaskia loam. The dominant tree on the 



' Soil Survey of Tama County, Iowa. U. S. Dept. of Agri., Bureau of Soils, 

 Washington, 1905. 



