MINING DISTRICTS 233 



and Shannon counties, with a preponderance of lead ore, but producing 

 some zinc ore, a small amount each of copper, nickle, and cobalt ores, 

 and locally large amounts of both red and brown hematite iron ores. 



5. The southern Missouri and northern Arkansas district, including 

 practically all the southern counties of Missouri west of Oregon county, 

 and three or four of the northern counties of Arkansas, particularly 

 Baxter, Marion, Boone, and Carroll counties, throughout which area 

 but little mining has been done in the true sense of the term, but which 

 contains " shines " or traces of lead and zinc ores exposed at the surface 

 in almost every county named. It is doubtful if there is a space as great 

 as 25 miles around this border which does not include very good surface 

 prospects for one or another of the ores mentioned. 



6. A few mining localities in southern Missouri, which lie outside of 

 what'should properly be called the border area, and in the high uplands 

 of the summit of the dome. Thus Aurora and Wentworth, in Lawrence 

 county, and Ashgrove, in western Green count}', with other less devel- 

 oped mines in southern Green county and northern Christian county, 

 should properly be looked upon as outside theborder area, with perhaps 

 other localities which may become of some importance in the future. Yet 

 the great preponderance of ore deposits as now developed are removed 

 from the summit of the uplift, with the richest ones occupying the outer 

 or lower portions of the border area. 



LlTHOLOGY AND AGE OF AREA 



VARIETIES OF ROCKS 



In lithologic characteristics the rocks included in the Ozark area are 

 of four principal varieties, namely, the Archean crystallines, limestones? 

 sandstones and conglomerates, and the flint or chert. 



ARCHEAN CRYSTALLINES 



These crystalline rocks are confined to the eastern part of the area con- 

 sidered, being extensively exposed in the southeastern mining district 

 as above outlined. They are granites and porphyries with basic dike- 

 rocks cutting them here and there in many places. The age of the dikes 

 seems to be pre-Cambrian, as they do not extend up into the overlying 

 Cambrian strata. Therefore the period of rock fracturing and volcanic 

 activity w T ith the outflows of lava producing the dike rocks was pre- 

 vious to Cambrian time and perhaps in no way connected with the sub- 

 sequent movements which produced the principal Ozark uplift. It is 

 probable that a floor of crystalline rocks extends westward under the 



