PREFACE. 



In the main, the brief descriptions that accompany the plates of this atlas are 

 synopses of the chapters of the corresponding plates in the respective volumes of the 

 final report; but not infrequently the reader will find in these descriptions not only 

 new ideas, but also somewhat different conclusions from .those of the original chap- 

 ters. This is because, up to very last, the survey has been also a development of 

 the geology of the state, and occasionally the earlier interpretations need to be mod- 

 ified. There is, however, nothing so discordant with the former chapters as to con- 

 stitute important departures from the views presented in the volumes containing 

 the detailed descriptions. In most cases attention is called to the fact, when the 

 theoretical part of the synopsis is based on new views. 



With these words the writer lays down his pen, after an unceasing labor of 

 twenty-eight years on this enterprise. While the survey, and the report in tout 

 ensemble, conform to the conception which he formed when he entered upon the 

 work, yet he is conscious of its numerous defects, and numerous lines of geological 

 research which have not been entered upon. He can, therefore, with strengthened 

 emphasis, repeat the following from the preface of volume I of this report: 



"At best this is but a preliminary investigation of the geology and geography 

 of the state. It adds definiteness and fullness to the work of Nicollet and of Owen; 

 but it rests on data, appliances and resources too limited and inexact to warrant the 

 expectation that the future will not find fault with it, and will not be able to extend 

 it by still more thorough and painstaking study. It is to be hoped, therefore, that in 

 the submission of this work to the scrutiny of the geologist of today, and to the 

 verdict of the geologist of the future, they will both scan its pages with due leniency 

 for its errors and imperfections." N. H. w. 



