GEOLOGY OF SOUTHWESTERN IOWA. 31 1 



At Anderson's mill on Clanton's branch of Middle river, in 

 the eastern part of Madison county, fig. 16. 



an exposure of strata was found which 

 is represented by Fig. 16, and is 

 evidently equivalent to that part of 

 the section at Clarke's, from one to 

 five inclusive, yet the different beds £i 

 are more subdivided. 



Section at Anderson's Mill. 



No. 8. Bluish shale with ferruginous concretions 4 feet. 



No. 7. Bluish, impure limestone 1% feet. 



No. 6. Bluish shale % foot. 



No. 5. Dark, carbonaceous shale 3^ f° ot - 



No. 4. Coal % foot. 



No. 3. Bluish, marly shale 8 feet. 



No. 2. Coal ... % foot. 



No. 1. Black, coaly, fossiliferous shale 3^ f° ot - 



The band of impure limestone, No. 7, is, no doubt, equiva- 

 lent to No. 2 of the Winter set section, and to No. 5 of the 

 section at Clarke's. This being the case, it will be seen that 

 the coal horizon, represented in those two sections, becomes 

 subdivided into thin seams in the eastern part of the county, 

 while it reaches its greatest development, so far as yet 

 ascertained, in the northern part of the county. Within a 

 couple of miles northward from Anderson's mill, a seam of 

 coal has been mined by stripping, which is no doubt the same 

 as one of those given in the Anderson's mill section, but the 

 associated seam was not observed there. The seam mined 

 there is only about nine inches thick. 



There are numerous other exposures of strata in different 

 parts of the county, but the foregoing are sufficient to give 

 the whole vertical range of those yet observed. Doubtless, 

 still lower strata than any here represented, occupy the 

 surface immediately beneath the drift in the northeastern 

 part of the county, but being soft or friable they have not 

 been exposed, or if so, have again become covered by their 

 own debris. 



