326 COUNTY AND KEGIONAL GEOLOGY. 



coal-measures, and almost entirely to the Upper. It will be 

 seen that no coal, not even the thinnest seam, is represented 

 in the foregoing sections, and it is not probable that any 

 exists among the exposed strata of the connty. It is evident, 

 therefore, that if coal is ever obtained in Decatur county, it 

 must be sought beneath the level of Grand river. Again, the 

 question comes — how deep must we go to reach a profitable 

 bed of coal ? This question cannot now be answered fully, 

 but the following suggestions are offered : 



It is known that at the western border of the Middle coal- 

 measure formation, as shown by Prof. St. John, in another 

 chapter, its thickness is about two hundred feet. There is 

 some evidence of a considerable thickening of the formation 

 to the southward and westward, so that it may possibly 

 reach three hundred feet in thickness in Decatur county. 

 Again, in the northern part of this formation it contains no 

 bed of coal of sufficient thickness to be worked with profit to 

 a great depth, although a number of thin ones are known to 

 exist there among its strata. We have indications, however, 

 that some of these Middle coal-measure coal beds thicken in 

 different directions, and they may probably be found of 

 profitable thickness when reached by sinking shafts to them 

 in this county. This, however, is doubtful, and the main 

 reliance for success in any enterprise of that kind should be 

 upon reaching the Lower coal-measures, the strata of which 

 are known to contain the thickest and best beds of coal. 



If explorations for coal by deep mining should ever be 

 undertaken in Decatur county, the work ought to be com- 

 menced in the valleys. This will save an amount of digging 

 and raising of the coal when found, equal to their depth 

 from the general surface. Grand river valley is the deepest 

 one in the county, and reaches the lowest strata to be found 

 exposed within its limits. These lowest strata, as would 

 naturally be inferred, are found in the southern part of the 

 county, and if coal is to be found within its limits, it is just 

 as likely to exist in that part as in any other; therefore the 

 chances are in favor of reaching coal there at less depth than 



