116 IOWA ACADEMY OF SCIENCE 



As recently shown 12 the Early Carboniferous section beneath 

 the Burlington limestone, in northeast Missouri, embraces more 

 than the three members originally ascribed to it. Two other 

 members properly belong to its base. This section presents the 



following succession : 



Feet 



Burlington limestone 



Unconformity. 



Chouteau limestone •. 30 



Hannibal shales 75 



Louisiana limestone 50 



Saverton (blue) shales 50 



Grassy (black) shales 40 



Unconformity. 



By reference to the principal cross-section (figure 8) it is noted 

 that the Chouteau limestone, which is a hundred feet thick at 

 the typical locality, gradually becomes thinner until it vanishes 

 completely just before the Mississippi river is reached, where the 

 Burlington limestone lies immediately upon the Hannibal shales. 

 On the other hand the Hannibal shales, which are seventy-five 

 feet in vertical measurement at the east end of the section, de- 

 cline in thickness westward until by the time Cooper county is 

 reached they disappear by attenuation, and the Chouteau and 

 (Louisiana members come together. The last mentioned lime- 

 stone, which is sixty feet thick at the Mississippi river, also be- 

 comes reduced to the west until in Cooper county it has only 

 about one-third its original measurement. It appears, therefore, 

 that Swallow 13 was actually correct in assigning the lower twen- 

 ty feet of the Cooper county "Chemung" (Kinderhook) to the 

 Lithographic (Louisiana) limestone. 



The Saverton shales, Grassy (black) shales, and the Snyder 

 (Devonian, Lime Creek) shales also chance to thin out towards 

 the west, so that at the western border of Cooper county the 

 Carboniferous limestones rest directly upon the Callaway (De- 

 vonian) limestones. Moreover, the Buffalo (Maquoketan) shales, 

 which are well developed on the Mississippi river, vanish com- 

 pletely within a distance of fifty miles of that stream. In central 

 Missouri there is, then, a rock succession extending from the St. 

 Peter sandstone to the Coal Measures that is without a single 

 shale or sandstone layer to relieve the limestone uniformity. 

 This is the reason why it is so difficult usually to interpret satis- 



J2 Am. Jour. Sci., (4), Vol. XXXVI, p. 160, 1913. 



"Missouri Geol. Surv., 1st and 2d Ann. Repts., p. 103, 1855. 



