298 COUNTY AND EEGIOISTAL GEOLOGY. 



They are the Drift, Bluff, and Alluvial soils. The drift soil 

 is much the most extensive, since it occupies almost the whole 

 of the region east of the East Mshnabotany river. The bluff 

 soil occupies the space between that river and the flood-plain 

 of the Missouri river. The alluvial soil of the region is, as 

 its name implies, that of the river flood-plains, principally 

 that of the Missouri river. 



2. THE MISSOURI RIVER BOTTOM. 



The great "bottom," or flood-plain of the Missouri is so 

 important, and so different from all other regions in the 

 State, that before proceeding to the separate description of 

 counties a general account of these alluvial lands will be 

 given. To make the description of these lands more 

 complete, the whole alluvial plain of the Missouri river will 

 be here discussed, so far as it forms a part of the surface of 

 our State, which even then will, of course, be understood to 

 comprise only a small part of the whole flood-plain of the 

 great river. Much the greater part of the flood-plain of that 

 portion of the river which borders upon Iowa, is upon the 

 Iowa side, and is continuous from the south boundary line 

 of the State to Sioux City, a distance of more than one 

 hundred and thirty miles. The river frequently runs near the 

 foot of the bluffs on the western or Nebraska side, but it does 

 so nowhere on the Iowa side, between the two points just 

 designated. On our side, the flood-plain varies from three to 

 twelve miles in width between the bluffs and the river. At 

 Sioux City, the bluffs rise directly from the bank of the 

 river, and as the latter bends away to the westward at this 

 point, and ceases to be the western boundary of the State, 

 the great flood-plain ends abruptly upon the Iowa side, just 

 below that city. 



This alluvial plain is roughly estimated to contain more 

 than half a million acres of land within the State of Iowa; 

 upward of four hundred thousand acres of which are now 

 tillable, or may be readily reclaimed to cultivation with little 



