The Missoiirian Scries of tJie Carboniferous. — Keyes. 299 
the subdivision to which the title was appHed was regarded as 
constituting one of the four great series making up the Car- 
boniferous. The name was selected for the reason that the 
Missouri river cut through, from top to bottom, the entire suc- 
cession of strata, and traversed the formation for a distance of 
more than 500 miles. 
Previous to obtaining the data for the exact correlation of 
the various parts of the Missourian series, the typical localities 
of the principal subdivisions of the Mississippian series, or 
lower Carboniferous,* and of the Des Moines series,f or pro- 
ductive coal measures, were visited and the relations of the dif- 
ferent formations carefully made out. A similar consideration 
of the Missourian series, or the third of the four major num- 
bers of the Carboniferous, is herewith given. 
The recent detailed examinations of the Missouri river ex- 
pCGures of the Carboniferous had, as its fundamental incentive, 
the establishment of a standard section to which all of the 
formations composing the Missourian series, in all parts of the 
latter's geographic extent, could be conveniently referred. 
The selection of this, rather than any other, line for the typical 
section of the series was influenced by a number of factors: 
first, the natural conditions were unusually favorable for corre- 
lating the various vertical sections not visibly connected ; sec- 
ond, there was furnished a reliable basis for future operations 
in the region; third, as most geological work is conducted 
more or less independently in the several states, a plan for uni- 
formity of methods and nomenclature was provided; fourth, 
the foundations were laid for a more general consideration of 
the geology of the region than had hitherto been attempted; 
fifth, the cross-section was as nearly transverse to the belt as it 
is possible to obtain; and sixth, a number of deep-well records 
furnished means of checking the extension of the formations 
below the river level. 
Historical Considerations. 
From the time when Nicollet]; made his explora- 
tions of the hydrographical basin of the Mississippi, 
in 1841, during which he descended the Missouri river 
*Bul. Geol. Soc. America, Vol. Ill, pp. 283-300, 1892. 
tProc. Iowa Acad. Sci., Vol. IV, pp. 22-25, 1897. 
JSon. Doc. 26th Cong., 2nd Sess., Vol. V, pt. ii, No. 237, 1841. 
