GEOLOGY OF SOUTHWESTERN IOWA. 313 



the city of Des Moines. Many new quarries may, without 

 doubt, be opened in this bed in the vicinity of Winterset, and 

 when railroads shall be built through this county, it will be in 

 good demand all along the lines of such roads. It will be in 

 especial demand in all those counties that are adjacent to 

 Madison, to the southward and westward. 



Common stone is so abundant in the greater part of this 

 county, that there will never be any lack of such material for 

 all necessary houses and outbuildings, the construction of 

 roads and bridges, the walling of wells and embankments; 

 and yet, the stone being exposed principally in the valleys, 

 the greater part of the surface is so unbroken and unobstructed 

 that it is tillable without difficulty. 



The clay represented by No. 3, of the Winterset section, 

 and which may be seen near the top of the high bank at the 

 ford two miles south of Winterset, may probably serve a 

 good purpose for common pottery, but potter's clay of the 

 best quality has not yet been observed in this county. 



Good brick clays are to be obtained in many parts, but 

 they are usually most accessible along the approaches to the 

 valley-sides where the soil is thin. 



It is worthy of remark, in passing, that the material found 

 among the Upper coal-measure strata of Madison and other 

 counties, and popularly called " slate," is not true slate, but 

 the black, fissile, carbonaceous shale represented by numbers 

 ten and twelve of the Winterset section. It splits readily into 

 thin layers of uniform thickness, in which condition it closely 

 resembles sheets of roofing slate, but it is practically worth- 

 less, as it soon exfoliates and decomposes upon exposure to 

 the weather. 



Coal. By turning again to the sections on the previous 

 pages, which represent all the strata exposed in Madison 

 county, it will be seen that with the exception of the compara- 

 tively thin bed of coal in the valley of North Branch, and its 

 representative near Anderson's mill, in the eastern part of the 

 county, there is no other in the whole series worthy of the 



name of a bed of coal. It has been shown, however, that the 

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