FLINT AREAS 235 



the borders of heavy flint areas limestone and flint are interbedded with 

 comparative regularity, the alternate layers being sometimes no more than 

 half an inch in thickness. Frequently, however, the flint has manifested 

 a tendency to assume rounded forms, as concretionary masses generally 

 do, so that boulders of many sizes and shapes are common, embedded in 

 the stratified limestone. It is not unusual for a drill or shaft to pass from 

 the surface to a depth of from 50 to 150 feet through limestone, below 

 which flint is found reaching to a much greater depth and bedded with 

 a considerable regularity. Such conditions are noted occasionally about 

 Galena and Joplin and Webb city, but perhaps most markedly so at 

 Wentworth and Aurora, at which places the principal ore deposits occupy 

 the open spaces between successive layers of flint. Around Galena and 

 Joplin the change in horizontal directions from flint to limestone may 

 be gradual or may be very abrupt, being so well marked that the dis- 

 tance of 100 feet will carry one from a solid flint area across to one of 

 correspondingly solid limestone; but such radical changes are excep- 

 tional. The fissures in the flint rock about Galena, Joplin, and Webb 

 city are the principal openings which have been filled with lead and 

 zinc ores. 



General Character of Ozark Uplift 



monoclinal type 



The Ozark dome in general is of the monoclinal type of uplifts so com- 

 mon in the great West, although the area is so small it represents the 

 type somewhat in miniature. It seems that the forces producing the up- 

 lift acted radially rather than tangentially and resulted in a stretch- 

 ing of the strata rather than a crumpling. On the summit the bedding 

 planes are found to be almost horizontal, while throughout the border 

 areas they are inclined away from the dome center. 



STRETCHING OF STRA TA 



The degree to which the strata were stretched or elongated has not 

 been measured accurately, but indications of it are found on all sides. 

 Winslow has noticed the tendency of the various fissures to contract 

 downward, although he does not particularly refer to the elongation of 

 the surface. Recently, while engaged in a study of the Kansas coal- 

 fields in the southeastern part of the state, it was learned that the so- 

 called "horsebacks," so abundant in the coalfields of Cherokee and 

 Crawford counties, are in reality clay-filled seams or fissures, produced 

 by earthquake movements, which trend parallel to the tangent of the 



