MIDDLE COAL MEASURES OP INTERIOR COAL FIELDS 



11 



mediate period which were recognized as the Middle Coal Measures, and, in the 

 absence of unconformity, it will he seen that there is a priori reason to expect a 

 series of beds- intermediate in character and position between the typical Des 

 Moines and the recognized base of the Missourian. All who have written on the 

 subject have recognized that the Coal Measures mark a continuous sequence of 

 deposition with only local breaks. Any divisions must be more or less arbitrarily 

 established, though they may, be none the less useful. 



The Des Moines beds, in the central portion of Iowa, consist of a thick mass of 

 shales and sandstones, showing no definite order of arrangement which may be 

 recognized over any considerable area, covered by a more regular sequence of which 

 the upper portion may be recognized over a considerable area; but as one travels 

 south two changes take place : (1) the upper member of the latter section thickens 

 from barely 30 feet on the South Raccoon to over 70 feet on Middle river near Win- 

 terset; (2) the various members of the section thin out, and are replaced until in 

 the southeastern portion of Madison county none of them can be made out. 



South from here in Clark and Lucas counties the work has not yet been carried 

 on in sufficient detail to allow a general section to be made out. It is, however, 

 known that there are in the region strata of the same general type as those found 

 in Madison, Dallas, and Guthrie counties, though probably detailed correlation 

 W'ill be impossible. 



Along the southern border of the state the Des Moines beds outcrop from the 

 Mississippi river west to Decatur county, where they become buried beneath the 

 Bethany. As fai- west as the Chariton river the beds may be referred unhesitat- 

 ingly to the lower division, corresponding with the Cherokee shales of Kansas. 

 Their character is shown in exposures and mine sections along the Chicago, Mil- 

 waukee and Saint Paul railway from Ottumwa southwest.* Above these is a for- 

 mation, including several limestone beds and one widely worked seam of coal, which 

 has been called the Appanoose formation.! In general chai-acter these strata cor- 

 respond to those seen farther north at the same horizon. 



As has been pointed out by Keyes,t there is a close correspondence between the 

 sections made out in Iowa, Missouri, and Kansas. These may be summarized as 

 below : 





Iowa. 



Missouri. 



Kansas. 



3 

 2 

 1 



No name 





Pleasanton. 

 f Pawnee. 

 1 Oswego. 



Cherokee. 



Appanoose 



Henrietta 











The Middle Coal Measures as originally defined included the two upper divisions 

 noted here. Swallow § recognized along the Missouri and at the top of his section 

 some 30 feet of sandy shales. White and St John found about the same thickness 

 along the Raccoon river. Between these two points it is now known that the sandy 

 meinber attains a considerable thickness and becomes sufficiently distinct to war- 



*Iowa Geological Survey, vol. v, plate xiv. 



t Iowa Geological Survey, vol. v, pp. 378, 394. 



X Proceedings Iowa Academy of Science, vol. iv, pp. 22-25, 1897. 



§ Geological Survey of Missouri, vols, i and ii, 1855, pp. 82, 83. 



