vi GEOLOGICAL SURVEY OF WISCONSIN. 



indicated, and these constitute the Area maps of the atlas. Seven of 

 these cover the territory reported upon in this volume. At least an 

 equal number will be required for the regions yet to be reported upon, 

 and these will be numbered consecutively with those now published, 

 so that the whole series, when complete, may form a single portfo- 

 lio. The contour lines of the topographical maps of the Lead region 

 required the still larger scale of one inch to the mile, and five plates 

 are devoted to them. 



It may be unnecessary to state that the construction of an ordina- 

 ry surface map is no proper part of the work of a geological survey, 

 and the geological corps cannot justly be held responsible for errors 

 of a merely geographical nature. When it is considered that the 

 original provisions of the law required the examination of more than 

 13,000 square miles each year, it will be evident that no work of that 

 kind was contemplated. But a correct geographical map is highly 

 important to accuracy in the delineation of the formations sketched 

 upon it, and hence the corps have labored under some annoying dif- 

 ficulties growing out of the inaccuracies of the original government sur- 

 veys, and of the maps in common use. To overcome these difficulties, so 

 far as possible, the Area maps have been built up, township by town- 

 ship, from the notes of the original linear survey of the government, 

 and comparisons instituted with state, county, township and special 

 maps, and with the observations of the geological corps. The townships 

 and sections should be, setting aside the convergence of the meridi- 

 ans and the trivial effects of sphericity, perfect squares, and cover the 

 state with a symmetrical network of lines, but it will be observed 

 that there are marked departures from this form in some cases, due 

 to errors in the linear surve} 7 , and an effort has been made, by care- 

 fully representing these on the maps, to restore the natural features 

 to their true form and position. 



The areas mapped as Wet Lands are essentially those given on the 

 government plats as marshes, but that term is not now properly ap- 

 plicable to a considerable portion of the surfaces so designated, since 

 most of them are so firm that they may be readily traversed by teams, 

 and some are even cultivated with success in all except very wet sea- 

 sons, and are, indeed, among the most valuable lands of the state. In 

 the great majority of cases, except where they are flu viatile meadows, 

 they represent extinct lakes, and hence their historical and geologi- 

 cal significance is important. 



The survey has been put under great obligations by the kindness 

 of citizens and corporations in rendering valuable aid in various ways 

 in the prosecution of the work. In addition to the more specific ac- 



