INTRODUCTORY 



LETTER. 



TO THE HON. J. BUTTERFIELD, 



COMMISSIONER OF THE GENERAL LAND OFFICE, 

 WASHINGTON. 



New Harmony, Indiana, 



October 30, 1851. 



Sir : — The Preliminary Reports, forwarded by me from time to time, have fur- 

 nished to the Department accounts of the field work ; while the Annual Reports of 

 1848 and 1849, heretofore submitted, contain a more full and digested statement of 

 the observations and discoveries of each year, made by the Geological Corps, in 

 Wisconsin, Iowa, and Minnesota. 



The Final Report, which I now lay before the Department, embraces, in a concise, 

 connected, and revised form, the substance of all the previous reports; together 

 with a full statement of the results of last season's operations : thus covering the 

 entire ground of the Survey. 



Condensed reports of the Assistant Geologist and of the heads of sub-corps, 

 accompany the present Report. These contain detailed descriptions of the districts 

 specially assigned to each ; together with generalizations deduced therefrom. 



In the estimation of heights, to be calculated in accordance with my instructions 

 above the level of Lake Superior, a long series of barometrical observations became 

 necessary. Some of these have been recorded in the form of meteorological tables, 

 supplying materials for comparing the climate of Lake Superior with that of the 

 Upper Mississippi, and showing the former to be milder and more equable than the 

 latter, and, indeed, than that of many portions of the United States, in much more 

 southern latitudes. 



I may here remark, however, that it has been my aim, during the entire conduct 

 of this exploration, to make the strictly practical and business portion of the Survey 

 the chief end and object of our operations. Scientific researches, which to some 

 may seem purely speculative and curious, are essential as preliminaries to these 

 practical results. Further than such necessity dictates, they have not been pushed, 

 except as subordinate and incidental, and chiefly at such periods as, under the 

 ordinary requirements of public service, might be regarded as leisure moments ; 

 so that the contributions to science thus incidentally afforded, and which a liberal 



