GEOLOGY OF SOUTHWESTERN IOWA. 315 



be found of sufficent thickness for profitable mining. Several 

 thin and profitless beds of coal would probably be passed 

 through within the first two hundred feet. It is thought 

 that the Sub-carboniferous limestone may be reached there at 

 a depth not exceeding five hundred feet, when of course 

 all further work should be stopped, as it is useless to look 

 for coal beneath or within that limestone formation. Thus it 

 will be seen that a limestone formation both underlies and 

 overlies the coal formations. 



Since all the strata rise gently and gradually to the east- 

 ward and northward, or rather the dip being in the opposite 

 directions, the lower ones of course come nearer the surface 

 in the eastern and northern parts of the county, and conse- 

 quently shafts of less depth would reach them from the 

 surface there. Therefore the Lower coal-measure strata, and 

 perhaps its bed of coal, may be reached at a less depth there 

 than elsewhere in the county. 



Such enterprises, if undertaken in Madison county, should 

 be watched with the greatest interest, because its success 

 would give additional confidence to those who may desire to 

 commence similar enterprises farther westward and south- 

 ward, and would tend to hasten the solution of the problem 

 of future supplies of coal in southwestern Iowa. 



As before stated, coal has already been found, and even 

 mined at a few points in this county, but all the coal thus far 

 discovered belongs to the thin beds of the Middle coal-mea- 

 sures before referred to, or to the thin seam represented by 

 No. 6, in the Winterset section. The former come to the 

 surface in the northern and eastern parts of the county, as 

 before explained. The thickest bed of coal yet found in the 

 county, is that at Mr. Clarke's bank, on JSTorth Branch, which 

 is reported to be at one point two and one-half feet thick, but 

 it is usually less. 



The same bed, but probably much thinner, may doubtless 

 be found within a few feet beneath the water level below 

 Compton's mill, one and a half miles from Winterset, and 

 also on land of Mr. McKnight, a mile or two below. On land 



