26 I'he American Geoioyiac. July, 1896 
Iowa and Missouri. Ahhoiij>-h minor subdivisions iiad been 
recognized it was not tliougiit necessary to s])ecilica]ly state 
tlie i'act until tlie wliole sequence liad been made <jut and 
aj)proi)riately defined. 
As a series tlie I)es Moines formation is perluips not so im- 
portant as any one of tlie other three mem))ers of the Carbon- 
iferous system, yet a knowledge of its stratigraphy will always 
be much more complete for the reason of the great economic 
value of its mineral contents and of the great extent to which 
these are being continuHlly sought. At the same time the 
series is, as compared with the others, much more complicated 
stratigraphically, its lithological characters change rapidly 
from place to place and from horizon to horizon, and its 
faunas and Horas are variable. In itself it is a very compact 
series, sharply set off from the other members both geologically 
and geographically. Although when Des Moines was first 
proposed as a geological term the formation was not referred 
to a specific vertical section nor its exact upper limits defined 
it was clearly stated and repeated subsequently* that it was 
sharply contrasted with the rocks of the next higher stage in 
lithological, stratigraphical and f;iunal characters, and that 
the change took place where the limestones began to come in. 
Soon after,! however, the superior line was located definitely 
at the base of the first great limestone, the Winterset lime- 
stone of Iowa and the Bethany limestone of Missouri. The 
upper delimiting horizon of the series is therefore the bottom 
of the limestone, which forms the basal member of the ovei'- 
lying series. 
'JMie nominal history of the Missourian series is essentially 
the same as tliat of the Des Moines. In using the name Mis- 
souri to designate ;J; a geological formation it was in the sense 
of covering all that had been previousl}' called the " up])er " 
Coal Measures. The lower limit was placedg at the base of 
the Bethany limestone. In neither Iowa nor Missouri was the 
full sequence represented and conse(i(uently beyond consider- 
ing it eo-extensive with the "upper Coal Measures" little 
*I()\va Geo!. Sur., vol. ii, p. 11!), 1894. 
tMissouri Geol. Sur., vol. iv, p. 82, 1891. 
JMon. Rev. Iowa Weather Service, vol. iv, p. ,3, 1893 ; and Iowa Geol. 
Sur., vol. I, p. 85, 1893. 
§Missoun Geol. Sur., vol. iv, p. 82, 1891. 
