128 PHYSICAL GEOGRAPHY. 



shown in Prof. Emery's report, it contains less than one per 

 cent of clay in its composition, it is in no respect inferior to 

 the best drift soil, and many of those who occupy it claim 

 that it is superior to any other. \ 



Its fertility is unquestionably as great as that of any, 

 while the advantage claimed for it is that it is perfectly under- 

 drained in consequence of the porosity and depth of the 

 deposit of which it constitutes a part, and containing no clay, 

 it never becomes heavy and " sticky," and never " bakes " in 

 times of drought. There being not a stone or pebble to be 

 found in it there are no obstructions to its perfect cultivation. 



3. ALLUVIAL SOILS. 



These are the soils of the Alluvial flood-plains of the river 

 valleys, or as they are popularly called in Iowa, "bottom 

 lands." They vary much in character and fertility, but the 

 best of them are the most fertile soils in the State, from the 

 fact that they contain the washings of the other soils, in 

 addition to a large amount of decayed vegetable matter 

 derived through the agency of former floods from the luxurious 

 growth along the borders of the streams. 



Those flood-plains, or portions of them, which are period- 

 ically flooded by their rivers are, of course, of little value for 

 agricultural purposes, but a large part of them are entirely 

 above the reach of the highest floods, while others are cached 

 only by extraordinary floods at intervals of several years. 

 Such as those last named are frequently cultivated, the farmer 

 estimating this occasional loss of a year's crop to be com- 

 sated for by the great productiveness of such soils in other 

 years. The lower portions of the flood-plains, even if they 

 were not annually reached by the floods of the streams, are 

 almost always too sandy for cultivation; but the higher ones 

 are usually covered with a fine silt which forms the soil, and 

 is often many feet in depth. The silt is almost always under- 

 laid by layers of sand and gravel, formerly deposited there 

 by the stream, so that the alluvial soils are usually well 



