34 FLUORSPAR DEPOSITS OF SOUTHERN ILLINOIS, [bull. 255. 



deformation apparently has been accomplished in part throngh 

 monoclinal folding rather than fracturing. At the Wright prospect, 

 near Rock, the sandstone and shale in the creek strike N. 60° E. 

 and dip 42° NW. About 500 feet farther west the strike is N. 45° 

 E. and the dip 40° SE. About a mile and a half east of Resort (sec. 

 9, T. 13 S., R. 5 E.) there is a considerable belt of limestone striking 

 N. 35° E. and dipping sharply to the southeast. Near the Luella 

 mines (sec. 10, T. 12 S., R. 6 E.) dips as high as 50° were observed, 

 and in a l)elt approximately parallel to the fault plane sandstone, 

 shale, and limestone pass successively beneath the surface. Near 

 Packers Gap (NE. i sec. 16, T. 11 S., R. 7 E.) heavy beds of sand- 

 stone striking N. 80° W. have a dip SW. 49° and show evidence 

 of some displacement between the beds. North of Elizabethtown on 

 th<e Patton land (sec. 21, T. 11 S., R. 9 E.) there is a belt of rocks 

 1.200 feet across, dipping 10° SE. and striking N. 30° E. The rocks 

 include sandstone, shale, and thin limestones, such as characterize the 

 Birdsville formation. There are minor faults and local evidences 

 of thrust. 



These varying dips are notably irregular, and in no case studied 

 did they indicate a regular system of folds. Occasionally, in connec- 

 tion with the displacement, comprehensive stresses have been gen- 

 erated, but these seem to have been entirely local in their effect and 

 incident to the general deformation by diverse displacement. 



GEOLOGIC HISTORY. 

 PERIODS or SEDIMENTATION. 



Of the pre-Devonian history of this area nothing is definitely 

 known. There are no exposures of earlier rocks in the district and 

 there are no drill records reaching below the black shale. In the 

 adjacent Ozark region, resting on pre-Caml)rian granites and por- 

 phyries, are Cambrian, Ordovician, and Silurian rocks, consisting 

 largely of nuignesian limestones, dolomites, and sandstones. The 

 contemporaneous rocks in the region south and east are largely non- 

 magnesian limestones and shales. In the absence of data it is uncer- 

 tain what kind of rocks were deposited here, and it can only be in- 

 ferred that in pre-Devonian time the area was one of sedimentation, 

 interrupted at intervals by periods of erosion. From Devonian until 

 late in the Carboniferous at least, similar conditions prevailed. At 

 times the area was covered by the sea and at times it formed part of 

 the land. The details of this history have not been made out, and,, 

 so far as known, are not significant from the present point of view. 



