G72 GEOLOGY AND TOPOGRAPHY OF THE LEAD REGION. 



contained in all the strata, irrespective of geological position, differ- 

 ing however considerably from the flint found in the Galena lime- 

 stone, in that they are more regularly segregated, forming layers by 

 themselves, and are not so promiscuously distributed through the 

 formation. 



The flint of the Lower Magnesian limestone is much whiter and 

 more liable to decomposition than that of the Galena. There are 

 also frequent geodes and cavities lined with drusy quartz-crystals, 

 which have never been seen in the Galena limestone, but are very 

 adundant in the Lower Magnesian. The crystals are of many colors, 

 white, yellow and rose color predominating, and often affording beau- 

 tiful cabinet specimens. 



A good general idea of the formation may be obtained from the 

 following descriptive section, taken from a bluff at the mouth of 

 Green river, on the Wisconsin, situated on the N. W. qr. of Sec. 22, 

 T. 7, R. 4 W. Upon the summit of the bluff, there was considerable 

 sandstone scattered about, although none could be found in place. It 

 was found in place on the other side of Green river at about the same 

 elevation, consequently we may assume that the top of the bluff is 

 quite near the top of the formation: 



A. Lower Magnesian Limesione. 



feet. 



1. Slope of hill (to top of vertical cliff) composed of heavy-bedded, light-gray, 



Magnesian limestone; stratification quite regular, contains no flints; good 

 building stone 23 



2. Hard, compact, heavy-bedded, light-colored limestone, lines of stratification not 



distinct; full of irregular masses of flint, which compose about half of the 

 bed; exposed in a vertical cliff 33 



3. Slope of hill covering limestone, not well exposed 23 



4. Coarse-grained limestone, weathering irregularly on exposed surfaces, contain- 

 ing a few flints disseminated through it, and occasional druses of quartz 7 



5. Gray limestone, very hard and compact, regularly stratified, beds from one to 



two feet thick, containing no flints 29 



6. Crystalline, gray, magnesian limestone, with a few flints irregularly dissemin- 



ated; beds two feet thick 9 



7. Hard, light-colored limestone, crystalline in texture, weathering but little on 



exposure; beds about three feet thick; contains no flints 46 



8. Fine-grained, straw-colored, slightly arenaceous, magnesian limestone; beds 



about one foot thick; stratification quite regular , 20 



9. Irregularly bedded, dplomitic limestone, has sometimes an oolitic structure 26 



10. Yellow, arenaceous limestone, transition beds. The sand appears in rounded 



grains, separate from one another, and cemented together with lime; strati- 

 fication indistinctly marked 23 



B. Potsdam Sandstone. 



11. Hard and compact sandstone, in beds from two to four feet thick, unfossiliferous, 20 



12. Very coarse-grained, yellow sandstone, weathering in rounded masses; exhibits 



cross lines of deposition; is very soft and friable 18 



13. Slope of hill probably covering sandstone 15 



14. Steep slope of hill to water in Wisconsin river; this is probably the place of the 



shaly, argillaceous layers 58 



Total thickness from water to top of the bluff 350 



Total thickness of Lower Magnesian exposed 239 



