618 GEOLOGY AND TOPOGRAPHY OF THE LEAD REGION. 



the report, so as to represent the topographical features of the country 

 with accuracy. The topographical maps herewith published embrace 

 all the Lead region. They comprise the country lying south of 

 town six, and extending from the Mississippi river eastward, to the 

 line between Rock and Green counties, with the exception of town 

 five in ranges 4, 5, 6, 7, 8 and 9 E. The maps are made on the scale 

 of one inch to the mile, and exhibit by contour lines, fifty feet apart 

 (vertically), the elevation of any point above the level of the sea. The 

 elevation of any point not on these lines must be determined by its 

 relative distance from the two contour lines between which it lies. 

 In addition to this feature (not found on any other map), a complete 

 road-map is presented; also a map of the streams and dry ravines, 

 many of the smaller streams having become dry since the original gov- 

 ernment survey of the country was made. Again, from an inspection 

 of these maps, can be seen the rise of the various streams, and the 

 height of the dividing ridges. This is also of special value in respect 

 to railroad surveys, when the amount of time and money is consid- 

 ered, which is annually spent in ascertaining these points. It is be- 

 leived that a tolerably correct idea of the practicability or impractic- 

 ability of any contemplated route can be obtained by reference to 

 these elevations, arid thus a vast amount of preliminary surveying 

 may be dispensed with. 



One of the principal objects of the field-work has been the careful 

 delineation of the geology of all parts of the country, and its correct 

 representation on the colored maps which accompany the reports. In 

 addition to the general geological maps of the state drawn on a scale 

 of three miles to the inch, the geology of the Lead region has also 

 been placed upon the topographical maps. The effect of this is to 

 show the dip and thickness of the strata and " the exact position of 

 the mining ground at each locality." The great extent of country 

 which has been examined and mapped, together with the time and 

 means which admitted of only a general survey, in which the contour 

 lines, both geological and topographical, could be sketched only by 

 the eye, preclude that accuracy which is attainable only with the tran- 

 sit and level. For such imperfections and inaccuracies as may be 

 found to exist in the maps, these circumstances must be our apology 

 and explanation. 



The geological sections accompanying the maps are chiefly valuable 

 as showing the " dip, number, magnitude, order and relative position 

 of the various strata," as well as the amount of denudation to which 

 the conntry has been subjected. They are located as far as- possible 



