260 GENERAL GEOLOGY. 



the Lower and Middle coal-measures, which together contain 

 nearly all the coal, extend beneath the unproductive coal- 

 measures to the western and southwestern parts of the State ; 

 and it is reasonable to infer that they contain their coal beds 

 there as well as where those formations occupy the surface. 

 It is possible that the Lower coal-measure strata occupy a 

 position nearer the surface in that portion of the State which 

 lies westward from Webster county, than they do farther to 

 the southward of that region; but since all the coal-measure 

 formations of the State thin out to the northward as well as 

 to the eastward, we should expect greater uncertainty of 

 finding coal there than we should in Pottawattamie county ; 

 for example, because the chances of finding a good bed of 

 coal are necessarily small near the thinned margin of the 

 formation or border of the field. 



After allowing for a very material thickening of the Upper 

 or barren coal-measures which probably occurs, in addition 

 to the already ascertained thickness of that formation along 

 its outcrop, there is good reason to believe that it does not 

 amount to enough to cover the productive coal-measures to a 

 depth at which it would be impractible to mine coal. From 

 examinations thus far made, it is estimated that a shaft of 

 one thousand feet in depth will pass through all the coal- 

 measure strata, productive and unproductive, at any point 

 from the base of the Drift Deposit within the State of Iowa. 



Therefore, there is reasonable hope that a shaft sunk for 

 coal at any point in Southwestern Iowa, will be attended with 

 success before reaching a depth so great as that at which coal 

 is profitably mined in other countries. If southwestern Iowa 

 were densely populated, capital abundant, and labor cheap, 

 as they are in older countries, capitalists knowing the relative 

 positions of the formations as before explained, would not 

 hesitate to incur the expense, great though it might be, of 

 sinking shafts of sufficient depth to prove the correctness or 

 fallacy of these inferences legitimately drawn from the results 

 of these investigations. 



Considering the present sparseness of population and 



