94 IOWA ACADEMY OF SCIENCES. 



souri river the Forbes limestone is carried down beneath the 

 water level. This trough is more than 250 feet deep, and per- 

 mits the Cottonwood limestone, for example, to extend east- 

 ward in a broad tongue more than forty miles farther than 

 would be ordinarily exp)ected. This being the case, the exten- 

 sion of the Burlingame limestone, as put down in the maps of 

 the Kansas geologists, meets in Nebraska the Cottonwood 

 limestone which is nearly 500 feet above. 



Atchison Shales. — In the most recent papers the name Wabaun- 

 see has been used in connection with the formation under consid- 

 eration. The latter name is derived from one of the counties 

 in central Kansas where the formation is well exposed. The 

 designation is that of Prosser,* for a sequence of shales that 

 occupy the interval between the Cottonwood limestone and the 

 Osage coals. It was subsequently made to include a few more 

 feet of shale below the last named horizon, and to extend to 

 the Burlingame (Forbes?) limestone. 



There seems to have been another name that has been used 

 in nearly the same sense as Prosser originally used Wabaun- 

 see. This will probably have to be substituted. As early as 

 1873, Broadhead designated the uppermost beds of the upper 

 coal measures as exposed in northwest Missouri, as the 

 "Atchison County Group." Subsequently he refers of ten to 

 them in this way. His descriptions of the lithological and 

 f aunal characters, though widely scattered, are very complete. 

 Re.<farding the stratigraphic position of the formation, it 

 reached from the summit of the Missouri section — now known 

 to be about 75 feet below the Cottonwood limestone — almost to 

 the Nodaway coal, which is nearly on the same horizon with 

 the Osage coal of central Kansas. The Atchison beds thus 

 have practically the same limits assigned to them as a quarter 

 of a century later Prosser proposed for the Wabaunsee. They 

 occupy over four-fifths of the interval that the Wabaunsee 

 occupies in the northwest corner of Missouri. For this reason 

 Atchison appears to be the only name that can be legitimately 

 used for the shales between the Forbes and Cottonwood lime- 

 stones. 



The Atchison shales are 500 feet thick on the Missouri river. 

 Near the base is at least one seam of coal of sufficient thickness 

 to profitably mine. This is the Nodaway coal, which has a very 

 considerable extent in northwestern Missouri and southwestern 



* Journal Geology, Vol. Ill, p. 690, 1895. 



