290 C. R. KEYES — THE PRINCIPAL MISSISSIPPIAN SECTION. 



Missouri the tipper portion is sandy in places and forms often a rather 

 compact, shaly sandstone, becoming harder northward, where it assumes 

 the character of a substantial sandrock. The latter is apparently entirely 

 absent in the southwestern part of the slate Downward, the shaly sand- 

 stone rapidly looses its arenaceous character and passes quickly into 

 bluish or greenish clay-shales winch appear remarkably uniform over 

 broad areas. At Burlington, Iowa, recent excavations show a thickness 

 of more than 70 feet, while borings indicate a thickness of double that 

 figure. Toward its known limit southward, in Greene county, Missouri, 

 for example, more than 50 feet of these shales have been observed, and 

 there is every reason to believe that they are considerably thicker. 



It is commonly supposed that these shales are destitute of fossils, bid- 

 late excavations at various places have disclosed rich faunas of a most 

 interesting and instructive nature. 



Chouteau Limestone. — The upper member of the Kinderhook is a fine 

 grained, compact limestone, buff in color, and usually more or less im- 

 pure from an admixture of clayey material. At Hannibal and Louisiana 

 it has a thickness of from 10 to 15 feet, apparently thinning out rapidly 

 northward. It is probably represented at Burlington, Iowa, by a few- 

 feet of buff calcareous layers lying at the base of the great limestone at 

 that place. At Legrand, in Marshall county, Iowa, the 50 feet of buff 

 magnesian limestone immediately underlying the Burlington may, per- 

 haps, be a northward extension of the Chouteau. Southward in Missouri 

 the bed in question increases in thickness until it attains a measurement 

 of 100 feet or more at Sedalia, and about 50 feet in the vicinity of Spring- 

 field in the southwestern part of the state. Near Ste. Genevieve there 

 arc probably from 75 to 100 feet of this limestone. It is quite possible 

 that in the northwestern part of this state, far below the Coal Measures, 

 this limestone attains even a much greater thickness. 



Osage Limestones. 



Definition and general Relations. — From a purely paleontological stand- 

 point, the advisability of including the Burlington and Keokuk lime- 

 stones under a single name was pointed* out several years ago. For 

 this long needed term Williams f has proposed "Osage." 



Owen's enerinital limestone embraced practically the same beds that 

 were afterwards called the Burlington,; and his lower Archimedes cor- 

 responded to Hall's Keokuk group below the geode bed. Shumard 

 seems to have used the term "Enerinital limestone" in a variety of 



*Am. Journ. Sei., 3d scries, vol. xxxviii. 1889, pp. 18G-193. 

 t Bull. U. S. Geol. Sur . no 80, 1891, p 169. 



