58 GEOLOGICAL SURVEY OF WISCONSIN. 



That the lead crevices, with their mineral contents, are not true 

 veins extending indefinitely downwards, but partake of the nature of 

 shrinkage cracks or joints, such as may be seen in almost all lime- 

 stone quarries. 



That though the mineral grounds have considerable lateral extent, 

 they reach only a short distance downwards. 



That the filling of the crevices with mineral matter was not from 

 below by volcanic heat, but from above, and by precipitation from a 

 solution. 



Much doubt and uncertainty still exist as to the origin of the 

 metallic sulphurets, and as to the time when, and the special condi- 

 tions under which they were introduced into these crevice joints. The 

 occurence of a similar lead region in southeastern Missouri, and of 

 another in the southwest part of the same state ; the first in the Lower 

 Magnesian limestone, the last in rocks of the Subcarboniferous age, 

 would seem to indicate either that these conditions were repeated at 

 three different times, or that they w r ere brought about at a time sub- 

 sequent to the deposition of the Subcarboniferous limestones. 



Attention is directed to the fact that the valley of Sugar river, 

 which constitutes the eastern boundary of the lead region, is much 

 broader and deeper in proportion to the amount of water at present 

 flowing in that stream than is usual; and hence the inference that at 

 some time in the remote past, a large river found its channel along the 

 course of the present Sugar river. With a breadth of stream of only 

 about one hundred feet, it has a valley as broad as that of the Missis- 

 sippi. In the future progress of the survey, additional light may be 

 thrown upon this subject. 



The information contained in this report with respect to the pres- 

 ent condition of the mines will have a practical value, and will con- 

 tribute much towards directing the attention of capital and enterprise 

 to that important industrial interest in our state. 



