20 GEOLOGY OF ILLINOIS. 



and crystalized masses in openings and caverns. The float 

 mineral is found in the red clay overlaying the lead-bearing 

 strata, and results from the decomposition of the upper 

 part of the lead-bearing rock, permitting the mineral to 

 settle down into the clays thus formed. The sheet mineral 

 exists in the form of thin veins in the solid rocks. The 

 crystalized masses are found adhering to the tops and sides 

 of caveins, or buried in the debris at their bottoms. The 

 granular and fibrous structure is almost wanting in this 

 lead region ; the crystaline is the only structure generally 

 noticed. 



The causes of the fissures in these lead rocks is supposed 

 to have been slow upheavals in the lead basin in past geo- 

 logical ages, and the dynamical agencies operating by rea- 

 son of the contractions and expansions of whole geological 

 formations. 



The historic sketch of 'mining for lead, found in the pub- 

 lished reports of the Illinois Geological Survey, although 

 far more indefinite than we could desire, is perhaps as per- 

 fect as we can make it. Many facts and statistics have 

 been lost; many items of interest were never preserved at all. 

 At the present time lead mining is in a tolerably flour- 

 ishing condition. The amount of mineral raised is not so 

 great as formerly, but the price is better. 



Two practical conclusions seem to have been arrived at 

 as a result of geological examinations in the lead region. 

 First, that no system of deep mining will ever be generally 

 adopted, simply because deep-buried bodies of mineral do 

 not exist. t Second, that a much better and cheaper way to 

 prospect for lead, is to drift into and across the veins by 

 adit levels, instead of sinking vertical shafts. 



In speaking of the Galena limestone, I have thus been 

 tempted to speak of the treasures lying aAvay in its dark 

 vaults. These vast bodies of metallic wealth have given 

 an interest and a name to this interesting formation. The 

 fortunes torn from its hidden fissures, and those yet to be 



