14 FLUOKSPAK DEPOSITS OF SOUTHEEN ILLINOIS, [bull. 255. 



SCOPE or THIS REPORT. 



The present paper is essentially a preliminary statement of results 

 based upon work done in 1903 in the Illinois portion of the Kentucky- 

 Illinois district. In this work the writer had the field assistance of 

 Mr. A. F. Crider, and the benefit of both field and office consultation 

 Avith Mr. E. O. Ulrich, whose tJiorough familiarity with the Kentucky 

 mines and the stratigraphy of the entire region contril)uted greatly 

 to the work. Mr. Albert Johannsen has furnished petrographic notes, 

 which are incorporated in the general description of the dike rocks.' 

 The report is intended to supplement the fuller discussion given by 

 Mr. Ulrich and Mr. W. S. Tangier Smith of the district in general 

 and the Kentucky mines in particular." Brief statements concerning 

 both portions of the district liave already been published.'' 



PHYSIOGRAPHY. 



GENERAL RELATIONS. 



The Kentucky-Illinois fluorspar district lies well toward the mid- 

 dle of the Mississippi Valley, that great level-floored basin which 

 occupies the continental interior of the United States. The district 

 is somewhat nearer the Appalachian than the Rocky Mountain bor- 

 der of the valley and about midway between the Great Lakes and the 

 Gulf of Mexico. The Mississippi Valley, though a monotonous plain 

 when contrasted with its surroundings, has been differentiated into a 

 number of physiographic provinces, which stand in somewhat marked 

 contrast with one anotlier. Of these, three— the Allegheny Plateaus, 

 the Gulf Plains, and the Ozark Plateau— meet within tliis district! 

 while the Prairie Plains join it on the north. 



The Allegheny Plateaus are represented l)v the Interior Lowland 

 as defined by Mr. C. W. Hayes.^ This occupies much of the mining 

 district in Kentucky and includes the upland between the Ohio R'uxn- 

 and Karbers Ridge, in Pope and Hardin counties. 111. The Gulf 

 Plains include the southern portion of Pope and the adjacent part of 

 Massac County, in Illinois, and that portion of Kentucky which lies 

 west of the Tennessee River. The more exact limits are shown, cov- 

 ered with Tertiary and Cretaceous deposits, on the accompanving oen- 

 eral geologic map of the district (PL I). The Ozark Plateau is rep- 

 resented by a long, narrow ridge of highland stretching across south- 

 ern Illinois from about Grand Tower, on the Mississippi, to Shawnee- 

 town, on the Ohk)^ This plateau is represented in Pope and Hardin 



" Prof. Papei- U. S. Geol. Survey No. 3fi, in press 



MTlrich and Smith. Bull. TJ. S. (Jeol. Survey No. 213. 190.3. pp. 205-213. Bain, Bull. 

 U. S. (.eol. Survey No. 225, 1904, pp. 505-511. 



-^ Hayes, C. W., Southern Appalachians ■ Mon. Nat. Geog. Soc, vol. 1, 1895, p. 310. 



