244 



GENERAL GEOLOGY. 



out to the westward within the State of Iowa, but dip 

 beneath the Upper coal-measure limestone to the southwest- 

 ward, the sub-carboniferous limestone previously having 

 passed beneath them, neither of which are to be seen again 

 in that direction. Thus the sub-carboniferous rocks do not 

 anywhere appear in the western part of the State, nor along 

 that part of the Missouri river-valley which borders Iowa, but 

 they are there hundreds of feet beneath the surface. It is the 

 rocks of the Upper coal-measure age alone that appear at 

 the surface there, if we except the Cretaceous strata farther up 

 the river. 



The next diagram, Fig. 14, shows the true relation of the 

 coal producing strata of Iowa to the two limestone formations 

 which respectively underlie and overlie them. This is also 

 still further illustrated both by the geological map-model, 

 and the lithographed plate of sections accompanying this 

 report. 



Fig. 14 



A, represents the Upper coal-measure limestone formation, which is almost 

 destitute of coal ; B, the Middle coal-measures with a few thin beds of coal ; C, 

 the Lower coal-measures which contains the most important coal-beds of Iowa; 

 •D, the St. Louis limestone, formerly but erroneously confounded with A; E, the 

 'Keokuk limestone ; F, the Burlington limestone, and G, the Kinderhook beds. 



Thus, instead of there being only one formation of Carbo- 

 niferous limestone, as has been supposed, and that dipping 

 beneath the coal-producing strata at the eastern border of the 

 coal-field of Iowa, and rising again from beneath them in the 

 western part of the State, the truth is, there are two separate 

 limestone formations, each possessing similar lithological, 

 but very different palseontological, characters ; the one over- 

 lying, and the other underlying the coal-producing strata. 

 The subject of the relative age of these formations will be 



