10 GEOLOGICAL SURVEY OF WISCONSIN. 



there have been disturbances of the strata, centers of elevation, etc., 

 questions of importance with regard to the downward continuance of 

 the veins, and the proper method of drainage. 



Mr. Strong's report will be found to contain much that is new and 

 valuable in regard to this important and very interesting district. 

 The local details, showing the present condition of the mines, and 

 their caijabilities of future production, cannot fail to be of great bene- 

 fit to the state by making known in a reliable form the advantages 

 that might be attained by a more vigorous prosecution of mining 

 operations at many of the localities described. 



The extent, physical characteristics, mineral contents, and other 

 important particulars of each rock-formation occurring in the district 

 examined, are clearly stated. The discovery of fossils in the Lower 

 Magnesian limestone shows that animal life was not entirely destroyed 

 during the epoch of the deposition of this great member of the Lower 

 Silurian series of rocks, and places it more directly in unison with the 

 Galena (or Lead-bearing) limestone from which it is only separated by 

 a comparatively thin layer of sandstone — the St. Peters. It thus 

 being shown to have one more character in common with that rock, 

 we may expect to find still more common features, such as the occur- 

 rence of crevices, openings, and the ores of lead, zinc, and copper. 

 Important facts are brought forward, bearing upon this question of 

 the occurrence of metallic ores of economical value, in the Lower 

 Magnesian limestone. 



Quarries of brown sandstone equal in beauty and value, and possess- 

 ing in many respects the same qualities, with that so much admired 

 from Lake Superior, are first publicly noticed in this report. 



Prominence is also very properly given to the layers of carbona- 

 ceous shale, containing from fifteen to forty-five per cent, of bitumin- 

 ous matter, which may, at some future time, be utilized in some way. 

 It was found that this shale occupies a position between the Blue 

 limestone below, and the Galena limestone above; and it thus be- 

 comes a ready means of determining the exact position of the mining 

 grounds, with reference to the geological formations. We have here 

 probable evidence of a considerable period of time during which vege- 

 table life — perhaps in the form of sea weeds — predominated, and 

 which may be regarded as an incipient effort towards the state of 

 things that long ages afterwards supplied coal and oil to the world. 

 ' The history of former efforts in the production of copper at Mineral 

 Point will be found interesting, and may lead to renewed efforts ia 

 that direction. 



With regard to the zinc ores — consist! )ig of the sulphuret (sphaler- 



