SURFACE FEATURES. 29 



southerly flowing rivers — the Mississippi on the east and the 

 Missouri, together with its tributary, the Big Sioux, on the 

 west. The northern boundary is upon the parallel of 43 

 degrees, 30 minutes, and the southern is approximately upon 

 that of 40 degrees, 36 minutes. The distance from the north- 

 ern to the southern boundary, excluding the small prominent 

 angle at the southeast corner, is a little more than two hundred 

 miles; and the extreme width from east to west is upward of 

 three hundred miles. Owing to the irregularity of the river 

 boundaries, however, the number of square miles does not 

 reach that of the multiple of these numbers, but according to 

 a statistical report of the Secretary of the Treasury to the 

 United States Senate, March 12th, 1863, the State of Iowa 

 contains 35,228,200 acres, or 55,044 square miles. 



2, GENERAL TOPOGRAPHY. 



No complete topographical survey of the State of Iowa 

 has yet been made, and no appropriation yet devoted to its 

 geological work would warrant its undertaking. Therefore, 

 all the knowledge we yet have upon the subject has been 

 derived from incidental observations of the geological corps, 

 from the published results of barometrical observations by 

 various persons in the employ of the general government, 

 and by levelings done by the engineer corps of the various 

 railroads within the State. By the use of data obtained 

 from these sources we attempt to give a general outline only, 

 of the topography of the State. We even omit here much 

 information that we possess concerning its details, a large 

 part of which, however, will be found under the heads of 

 Rivers, Lakes, Surface Deposits, etc. Railroads have already 

 become so numerous in Iowa, that we are able to derive from 

 their levelings alone a very correct general knowledge of the 

 topography of our Commonwealth. Fortunately for the 

 Geological Survey, the chief engineers and other officers of 

 these roads have cheerfully and gratuitously furnished all 

 desired data for this purpose, in the form of lists of the 

 elevation of points along their respective lines. All these 



