BAIN.] MINES AND PROSPECTS. 43 



Age. — The ores were formed after the period of deformation, 

 which, as has already been shown, was hite in the Carboniferous or 

 after the close of that period. They originated before the Lafayette 

 peneplain was cut, and they do not seem to be forming now. They 

 may be as old as the Permian or as young as middle Tertiary, but it 

 is impossible to fix their age more definitely on the basis of local 

 evidence. 



Genesis and vahie. — These topics will be discussed in detail after 

 the description of the individual mines. 



DESCRIPTION OF MINES AND PROSPECTS. 



EOSICLARE AREA. 



Resume of geology. — The formations exposed near Rosiclare have 

 already been discussed, but a brief resume with certain additional 

 details will help in understanding the jnine descriptions. 



The southeastern portion of the area (PL II), extending from 

 Elizabethtown to Orr's landing and back to the crossing of Big 

 Creek by the Golconda road, is underlain by the St. Louis limestone. 

 This formation is brought into faulting contact with the Chester 

 formations, though probably in part at least the boundary between 

 it and the Ste. Genevieve is a normal erosion boundary. So far as 

 known no ore bodies have been found in the St. Louis of this vicinity. 

 Small amounts of fluorspar occur in cavities in the rock, and there are 

 several well-developed veins of calcite, the more prominent ones being 

 represented on the map. 



The central portion of the area is underlain by a broad belt of 

 Chester formations trending northeast and southwest. These are in 

 part in faulting contact with each other. Only the Ste. Genevieve 

 limestone is ma})ped separately. The beds have a very gentle dip to 

 the northwest, the highest beds noted being in sections 30 and ?>1. 



The Mansfield sandstone occupies the northwestern corner of the 

 area, and the irregular boundary, the presence of outliers, and the 

 absence of faulting phenomena indicate that it rests upon the Chester 

 with a normal erosion contact. 



Igneous rocks outcrop at three points along the Ohio, cutting the 

 St. Louis and Ste. Genevieve limestones. There are two other doubt- 

 ful occurrences known. 



The veins occur along faidt planes having in most cases a northeast- 

 southwest trend and falling within a single vein system crossing the 

 area from section 8 to section 21. The area has up to the present 

 proved the most productive in the wliole district, but this may have 

 been due as much to the nearness of the mines to the river as to the 

 size of the ore bodies. 



