IOWA ACADEMY OF SCIENCES. 
25 
shales. Had this teroi been defined in any way it would prob- 
ably have to be adopted as the designation of the formation. 
Subsequently Haworth* without the slightest reference to this 
title, and without a very much, better definition for the new 
name changed it to Pleasanton shales. As in a later publicationf 
the latter term has been more clearly limited and applied, it 
should probably be regarded as the proper designation of the 
formation. 
In Iowa there are recognizable in the Des Moines series (1) 
an upper shale bed of considerable thickness, which lies 
beneath the Bethany or Winterset limestone, (2) a lower shale 
bed, 300 to 400 feet thick which rests on the Mississippian and 
older strata, and (3), between the two, a seii of beds that includes 
limestone layers which, though comparatively thin, rarely 
more than four to six feet, are of relatively great lateral per- 
sistency and carry at least one seam of workable coal. In 
southern Iowa the last mentioned beds appear to be best 
developed in Appanoose county and the adjoining districts. 
The Mystic coal, the seam having the greatest areal extent of 
any in the state, is included in this median member. The lime- 
stone beds are closely associated with the coal. The strata 
have a total thickness of perhaps seventy- five feet. They indi- 
cate an epoch, during which temporarily, marine cor ditions pre- 
vailed to a greater extent than during any other time between 
the secession of Mississippian deposition in the region and the 
introduction of the Missourian. 
The exact relation between these particular subdivision lines 
of the strata of Iowa and of southwest Missouri have, of course, 
not been directly traced in detail, but the close resemblance of 
the vertical sections is so striking and the probabilities of their 
being equivalent are so great that it seems worth the while, at 
this time, to call attention to the facts, while the top and bot- 
tom of the Des Moines series, as a whole, has been clearly 
made out over the entire region. 
^Kansas Uaiv. Quart., vol. Ill, p. 274, 1895 
tUniv. Geol. Sur., Kansas, vol. I, p. 153, 1896. 
