Soil Survey of Cass County, Indiana. 195 
The immediate subsoil consists of a yellow or yellowish brown silty 
clay loam having a depth of from twenty to thirty inches. This is 
immediately underlain by a yellowish clay or yellowish gritty or sandy 
loam with usually more or less amount of coarse sand, gravel and 
boulders. As a rule the material consists chiefly of fragments of lime- 
stone, a mixture of crystallines of various kinds. 
The silt loam has a more brownish color near the streams, where 
the ground is more or less broken, and on the well-drained ridges. This 
is due to greater oxidation because of better drainage. The white clay 
knolls will take on a darker color when better drained and aerated. 
The different soil areas mapped as the Miami silt loam will vary 
from the above description in one or more particulars, but will agree in 
the main. The Miami silt loam has a level to undulating or rolling 
surface and occurs throughout the country, with the Clyde series occur- 
ing in the depressions. 
Origin—The Miami silt loam, in common with other members of 
the Miami series, is due to the glaciation of the region in which it 
occurs. The retreating ice left the till with a very uneven surface, 
composed of numerous ridges and valleys or depressions. During the 
process of erosion and weathering since that time, the ridges have tended 
to become lower, thus filling the depressions with the organic remains 
and the finer sediments from the higher lands. The better natural 
drainage and lack of a large amount of humus would preduce a light- 
colored soil with a high clay and silt content. This condition is well 
- shown along the larger watercourses, where the surplus water rapidly 
drains away, producing a wide strip of the Miami series on either side 
without any or with very few areas of the Clyde series even in the 
largest depressions. 
Drainage.—The fine texture and uniform structure causes ground 
water to move slowly and makes natural drainage inadequate in the 
Miami silt loam. This condition can be remedied by the use of tile 
drainage, but care should be taken by not using too small tile as lateral 
lines. The drains not only remove the surplus water in wet weather, 
thus lowering the ground water table, but also help to aerate the soil 
in dry weather. In most cultivated soils the pore space is from 25% 
to 50% of the volume, and this is the maximum water capacity or satu- 
ration capacity. The amount of this space occupied by water for the 
maximum development of most plants is from 40% to 50% of the pore 
space, which leaves one-half or more to be occupied by air. The pres- 
ence of a large amount of oxygen in the soil is essential to the best 
growth of the plant crops as well as the liberation of the necessary 
plant food. 
