36 FLUORSPAR DEPOSITS OF SOUTHERN ILLINOIS, [bull. 1255. 



The upland plain i)reviously discussed marks the last of the im- 

 portant cycles of erosion, and its age has already l)een suggested 

 to be Lafaj'Ctte or late Tertiary. At the completion of this cycle 

 Karhers Kidge, tlie Shetlerville Hills, and certain areas in Kentucky 

 renuiined as monadnocks rising above the plain. Since its comple- 

 tion the country has been elevated as a whole 200 feet or more, and 

 the streams have cut their present channels. This elevation seems 

 not to have been continuous, since there are traces of incomplete 

 peneplains below the main one 'and above the bottoms of the rivers. 



TIIK OKE DEPOSITS. 



GENERAL CHARACTER. 



The ore deposits of Pope and Hardin, counties are vein deposits 

 occurring along faulting fissures. The vein material consists essen- 

 tially of fluorspar and calcite, or " calc spar," as it is locally called. 

 Associated with these minerals are minor amounts of the lead and 

 zinc sulphides, galena and blende. There are also traces of other 

 sulphides, notably those containing co])[)er and antimony. Surface 

 alteration is relatively unimportant, though some carbonate of zinc 

 occurs, and in the adjacent portion of Kentucky one or two bodies of 

 it ha\(' been mined. No traces of secondary enrichment have been 

 observed. AVithin the area ar(^ certain bodies of limonite. which yvere 

 formerly mined, but which are now unimiK^rtant. Fluorspar is the 

 only mineral now mined in (jua.ntity, and the deposits afford, there- 

 fore, an instance of what is ordinarily, and was here originally, merely 

 a gangue mineral, !>eing ihe one whicli gix'es value to the ore. 



MINERALS PRESENT. 



<;an(Uik isiiNKitAns. 



Fliioi'/tc. — This district is cliaracterized b}^ the peculiar and remark- 

 able al)uudance of the calcium fluoride, CaFo, correspcmding in com- 

 ])osition to 51 per cent of calcium and 49 per cent of fluorine (spe- 

 cific gravity, -kOI to 3.25). This mineral occurs in large bodies of 

 unusual ])urity, shipments running i)8 to 99 jjer cent being constantly 

 made. Very little running less than 95 per cent finds sale excej)t at 

 reduced })rice. The mineral is crystallized, and in druses and open 

 spaces well-developed crystals are not unconnnon. On these the 

 faces of the cube are best developed, but modifications due to the 

 octahedron may be frequently noted. For the most part the fluorite 

 occurs in great vertical sheets or veins clearly crystallized, but not 

 showing crystal form. The octahedral cleavage is always well devel- 

 oped, so much so, in fact, that jig concentrates consist largeh^ of 

 im})erfect tetrahedra aiul octahedra. Cleavage forms are easily ob- 



