54 FLUOBSPAR DEPOSITS OF SOUTHERN ILLINOIS, [bdll. 255. 



Gordon mine. — On the same quarter section and possibly on the 

 same vein as the Parkenson is the Gordon shaft, also not being worked 

 when visited. Here, again, the sandstone shows some brecciation, 

 and fliiorite, calcite, barite, blende, and galena occur. The barite and 

 blende seem to be especially abundant and are apparently of good 

 grade. 



Lead Hill. — Al)out ?> miles from the river, at Cave in Rock, there 

 is an abrui)t rise of 80 feet and a mural escarpment fronts the irreg- 

 ular plain developed o^er the area of St. Louis limestone. At the 

 foot of this escarpment and parallel to it is a fault which may be 

 traced somewhat south of east for nearly 3 miles. Along this escarp- 

 ment, particularly in sections 3 and 4, T. 12 S., E. 9 E., mining has 

 been carried on for a number of years, and formerly enough lead was 

 taken out to give its name to the locality. 



In 1903 the Cleveland-Illinois Fluorspar Company was operating 

 a mine about on the line between sections 2 and 3. The company was 

 Avorking a bedded or sheet deposit in tlie Fredonia member of the 

 Ste. Genevieve limestone and just under the Rosiclare sandstone. 

 A number of short drifts were run into the hill, and the workings 

 were conducted on a modified room-and-pillar S3^stem. The ore 

 body varies in thickness from 18 inches to 6 feet, thinning as the 

 workings extend into the hill. The vein stuff consists to a minor 

 extent of brecciated limestone, but for the most part of interbandecl 

 limestone and fluorite with minor amounts of calcite and galena. 

 At the to]^ of the ore there is a band of green sandy shale a few inches 

 thick, and the fluorite extends into this between the laminae. Brec- 

 cia is only locally developed, and banded limestone and fluorite, 

 such as is illustrated in PI. V, is more common. In this specimen 

 the individual bands of purple and white fluorite are one-half to 

 three-fourths of an inch thick, and are separated by layers of equal 

 thickness made u}) of very impure limestone containing notable quan- 

 tities of silica and iron oxide. This banding represents horizontal 

 bedding, and the fluorite has evidently been introduced along the 

 stratification planes, uniting with the calcium of the limestone and 

 excluding the impurities. These were partly, no doubt, carried off, 

 but also in part remain traj^ped between the growing crystals of 

 fluorite and in the bands of unreplaced limestone. 



These relations are perhaps made clearer by the photomicrographs 

 of PL VI. In .1 is shown, in natural light, a portion of one of the 

 fluorspar bands. Traces of bedding may be observed, and the iron 

 oxides and other impurities are so arranged as to mark the outlines of 

 granular material, presumably the original calcite. 



In B the same section is shown between crossed nicols. The fluor- 

 ite appears entirely black, while the small points of light indicate 



