34 IOWA ACADEMY OF SCIENCES. 



The limitations of tlie various strata are perhaps more strikingly shown 

 in the coal beds themselves than in any others. The fev^r limestones known 

 to occur in the liOwer Coal Measures, such as that shown in the banks of 

 Walnut Creek at Mystic, are of course persistent over wide areas. Certain 

 of the sandstones, such for example as that exposed at Red Rock, in Marion 

 county, attain a considerable geographic extent. The shales, however, and 

 even more particularly the coal beds, usually cover areas quite limited. 

 Indeed it is the exception to tind a coal bed which can be traced more than 

 a few miles at most. 



In marked contrast to this general character is the coal seam at present 

 worked in Appanoose and adjoining counties. As compared with the other 

 coal seams of Iowa the extent of the one in question is quite exceptional. 

 As nearly as can now be determined it extends over a distance of nearly 

 fifty miles north and south and at least forty miles east and west. There is 

 probably no other vein in the Lower Coal Measures of the State which 

 extends unbroken over an equal stretch of territory. Not that it is now 

 absolutely continuous over the whole extent, but that its identity may be 

 accepted with considerable assurance. 



A general section representative of the strata of this i-egion taken from 

 the record of several mines at Centerville is as follows: 



FEET. INCHES. 



17. Soil, fine black 3 



16. Clay, yellow 33 



15. Clay, blue, containing boulders and fragments of wood, coal and 



limerock 30 



14. Limestone 6 



13. Shale, argillaceous, blue 3 



12. Shale, argillaceous, red 11 



11. Sandstone, soft with thin hard layers 8 



10. Shale, argillaceous 10 



9. Limestone, compact gray 3 



8. Shale, bituminous pyritiferous 7 



7. Limestone, usually bituminous "Caprock" 3 6 



6. Shale, firm bituminous 1 2 



5. Coal 1 8 



4. Clay-parting 2 



3. Coal 1 2 



2. Fireclay 3 



1. Limestone (seen in the bluffs at Mystic) 2 10 



The thickness and character of these different layers vary within certain 

 limits, but the general features of the section may be considered as fairly 

 constant. Other bauds of limestone occasionally make their appearance, 

 and the character of the shale is of course inconstant. The presence of 

 numbers 9 and 14 is tolerably constant throughout the field. They are known 

 respectively as the "Seventeen" and "Fifty foot" limestones from their general 

 occurrence at about those heights above the coal. They may be relied upon 

 as fairly accurate guiding marks, though they have in certain places been 

 removed by later erosion. 



An examination of the coal in the above section shows that it.has several 

 points which ai'e peculiarly chai'acteristic, and make its recognition easy 

 and secure. 



The following five sections are taken from different parts of the field, and 

 are a few of a large number showing the characteristics of the vein. They 



