PART I. 



PHYSICAL GEOGRAPHY 



CHAPTER I. 



SURFACE FEATURES. 



1. BOUNDARIES AND AREA. 



In consequence of the generally nniform character of trie 

 snrface of trie region which comprises the upper portion of 

 the great hydrographical basin of the Mississippi, its linear 

 surveys have been made with great facility, and were further 

 greatly simplified by the peculiar system adopted by the 

 general government when the surveys were ordered. The 

 system is well explained in an appendix to this volume by 

 C. W. Irish, Esq., and frequent reference is made to it 

 throughout the text, because these linear surveys were con- 

 stantly used as a basis for geological observation. This 

 system has given rise to a general prevalence of rectangular 

 boundaries of all the subdivisions of land extending from 

 the nearly uniformly mile-square sections, up through the 

 townships and counties, and has produced more or less 

 rectangular outlines of the States also. The latter, however, 

 have always some portions of their boundaries modified or 

 determined by natural features, such as rivers, lakes, etc. 



The State of Iowa has an outline figure nearly approach- 

 ing that of a rectangular parallelogram, the northern and 

 southern boundaries being nearly due east and west lines, 



and its eastern and western boundaries determined by 



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