236 E. HAWORTH — THE OZARK UPLIFT AND ORE DEPOSITS 



Ozark elliptical area. The brittle coalbeds readily break, and, being 

 dark in color, are most excellent indicators of earth movements. It was 

 found that the stretching of .surface lines had resulted in opening these 

 numerous fissures to distances varying from 3 to 30 or 40 feet. It was 

 further observed that such fractures were rarely accompanied by vertical 

 displacement, although one mine near Pittsburg showed a displacement 

 of 8 feet, the downthrow being- to the east. The coalbeds to the north 

 and northwest have a much smaller number of " horsebacks " or fissures, 

 the number growing smaller as the distance from the Ozarks increases, 

 until at Osage city and Leavenworth they are entirely unknown, strongly 

 implying that the fissures in Cherokee and Crawford counties were con- 

 nected in origin with the Ozark uplift. 



THE FRACTURES 



The fractures appear to be much more numerous around the borders 

 of the uplifted area than in the central part. About Galena and Joplin 

 the flint rocks are so badly shattered that it seems to be impossible to 

 find a fragment 6 inches in diameter free from fissures. The " ribbed " 

 ground is here the prevailing type, so called on account of the great 

 abundance and general parallelism of vertical fissures. To the east at 

 Wentworth and Aurora, nearer the summit of the dome, the heavy flint 

 beds carrying the ores are almost free from fissures and the " ribbed " 

 condition is entirely wanting. A careful study in other parts of the area 

 would probably reveal a similar set of conditions. It is known that 

 fissures are frequently found along the northern border in Hickory, 

 Morgan, and adjacent counties, producing true fissure veins. The same 

 is true to a considerable extent in the southeast about Bonne Terre and 

 Mine La Motte, while northern Arkansas and southern Missouri, although 

 less extensively studied, reveal much the same condition. This is in 

 accord with the general conditions observed elsewhere in areas occupy- 

 ing great monoclinal uplifts, the areas of maximum fracturing and fault- 

 ing being confined to the borders. 



It is probable that the nature of the rocks had a strong influence on 

 the character of the fissures produced by earth movements. The heavy 

 beds of Silurian limestone, with cushions of soft interbedded sandstone, 

 would resist fracture tendencies as well as any rocks known; but when 

 the stress became sufficiently great to produce fracturing the tough and 

 somewhat elastic limestone would yield, producing a small number of 

 relatively large fissures, accompanied by vertical displacement or other- 

 wise, thereby relieving the strain. The opposite extreme is found in the 

 heavy beds of brittle flint about Galena and Joplin. Here the slightest 



