MISSTISSIPPIAN CHERT OF ST. LOUIS AREA 367 
indifferently in fine-grained, even lithographic limestones, and in 
coarse-grained ones. It is found in massively bedded as well as in 
thin-bedded limestones. It is not found, to the writer’s knowledge, 
in pure or only slightly calcareous sandstones or shales, but is found 
in arenaceous and argillaceous limestones. It is found in highly 
magnesium limestones and in very pure limestones. A series of 
analyses of the chert-bearing St. Louis and Burlington-Keokuk 
limestones at St. Louis show a variation in composition as given 
in Table I. 
TABLE I* 
Limestone SHE Recdde PnOnaE CaCOs MgCO; 
SP yIEOUISS ae ee oss 1.48-9.56 0.35-1.82 61.88-94.97 | 0.94-24.53 
Burlington-Keokuk....| 1.10-4.35 ©.40-1.82 77.95-94.50 | 3.18-14.84 
*Anaiyses by A. E. Atwood, Geol. Surv. of Missouri, Bull. No. 3 (1890), p. 77. 
CONTEMPORANEOUS CHERT OF OTHER AREAS 
In areal distribution these Mississippian cherts are not restricted 
to the St. Louis area, but are widespread and are characteristic of 
the St. Louis limestone and equivalent formations and the 
Burlington-Keokuk limestone and equivalent formations practically 
wherever they are found. The Salem limestone of the St. Louis 
area is free from chert, as is also the Bedford odlite, its equivalent 
to the east. The exact extent of the distribution of the chert in the 
St. Louis limestone and the Burlington-Keokuk limestone is best 
shown graphically in Figs. 3 and 4, on which are plotted the outcrops 
of these formations and the areas in which they are chert-bearing. 
The correlation of formations on these maps is taken largely 
from B. Willis’ “Index to the Stratigraphy of North America,” 
U.S. Geol. Surv. Prof. Paper 71. While the morphology of these 
equivalent chert beds varies somewhat from locality to locality, yet 
there seems to be a greater or smaller constancy of habits of the 
chert of each formation. The St. Louis is characterized by even, 
ball-like chert even to Alabama, while the Lauderdale is spoken of 
as platelike, and the Boone chert and Grand Falls chert of western 
Missouri are said to be lenslike or sheetlike. It is perhaps worthy 
