66 GEOLOGICAL SURVEY OP WISCONSIN. 



He was thus fortunately able to accomplish the whole of the work 

 assigned to him at the beginning of the season, and to prepare his 

 second annual ;jeport, with the necessary maps, sections and diagrams, 

 within the time prescribed by law. 



The work of the past season is so intimately connected with that of 

 the previous year, that it was deemed best to include the whole in 

 one report; accordingly this has been done by Mr. Strong, so that the 

 accompanying report gives one connected and comprehensive view of 

 his work, and its results up to the present time. 



In this report will be found full details with respect to the district 

 thus surveyed, arranged under the following heads : 

 Previous publications and surveys ; 

 Topographical and geological maps and sections ; 

 Earometrical observations; 

 Physical geography, and surface geology; 

 The several rock formations; being the 

 Potsdam sandstone, 

 Lower Magnesian limestone, 

 St. Peters sandstone. 

 Buff and Blue (Trenton) limestone, 

 Galena limestone, and 

 Cincinnati group. 

 All considered with respect to their geographical boundaries, litho- 

 logical character, ores, minerals and paleontology; 

 The origin of river valleys ; 

 Explanation of mining terms ; 

 Present condition of the mines; 

 Statistics of lead, zinc and copper production; 

 Explorations north of the Wisconsin river, and 

 Prehistoric mounds of the lead region. 

 Topographical maps accompany this report, embracing the entire 

 lead region, on a scale of one mile to an inch, which is sufficient to 

 exhibit, by contour lines fifty feet apart (vertically), the elevation of 

 every point above the level of the sea. These maps also show the posi- 

 tion of the public roads. Such maps have special value not only in 

 respect to future railroad surveys, showing at once the practicability 

 or impracticability of any contemplated route, and thus save the time 

 and expense of a very large amount of preliminary surveys, but are, 

 obviously, of great importance to the mining interest, as indicating 

 the proper system of di'ainage, location of "levels," etc. Geological 

 maps are also furnished, constructed upon the same scale, showing the 

 position of the several rock formations, by which the relation of a ly 



