THE FRACTURES 237 



strain would produce fractures in a rock as brittle as glass, already pos- 

 sessing internal tensions of a high degree, so that the required yielding 

 would be along the lines of myriads of small fractures rather than along 

 a few large ones. Large fissure veins and faults of appreciable size 

 would therefore be less frequent than in limestone regions. 



But the numerous small fissures would permit weathering agents to 

 pass downward much more generally than in regions of the larger fissures, 

 which, in connection with the interbedded character of the limestone 

 and flint, would cause a much greater dissolving out of the limestones 

 than elsewhere. This in turn would increase the underground openings 

 and bring about to a great degree a falling in of the residual flint masses, 

 resulting in the production of great disturbance, with a maximum oppor- 

 tunity for free circulation of ground waters, one of the essential condi- 

 tions for extensive ore deposition. 



It is a noteworthy fact that the whole Ozark disturbance was unaccom- 

 panied by volcanic action of any kind whatever, as far as is now known, 

 save the one little instance in Camden county where a pegmatite dike 

 was discovered by Winslow, with the Mesozoic eruptives of Arkansas 

 being the only other instance known in the whole Mississippi valley of 

 post-Paleozoic volcanic action. 



Mineralization of the Rocks 

 its character 



The mineralization which has taken place has a dual interest, one on 

 account of the character of minerals formed and one on account of the 

 absence of certain other minerals frequently found in areas of great 

 disturbance. 



LIST OF MINERALS AND ORES 



In the western, northern, and southern parts of the area the ores found 

 are : galena, with its well known alteration products ; zinc blende, with 

 its customary alteration products ; copper pyrite and secondary mineral, 

 resulting from its weathering; the two iron sulphides, pyrite and mar- 

 casite, and their decomposition products ; calcite, dolomite, barite, and 

 quartz, with possible traces of a few other minerals not yet-observed. In 

 the southeastern district, in addition to those just named, the different 

 iron oxides are found in large quantities, with ores of both cobalt and 

 nickel, and in at least one fissure vein with granite walls at the old Ein- 

 stein Silver Mines different fumerole minerals, such as quartz, fluorite, 

 topaz, wolframite, and lithia-mica, have been found. In the west quartz 

 is almost entirely unknown, only a few specimens of well crystallized 



