THE 
AMERICAN NATURALIST 

VoL. XXIV. APRIL, 1890. 280. . 

ON THE BRECCIATED CHARACTER OF THE ST. 
LOUIS LIMESTONE. 
BY C. H. GORDON. 
N the absence of the Chester, the St. Louis beds constitute the 
uppermost division of the Subcarboniferous in Iowa. They 
consist generally of limestone above, yellowish-gray, more or less 
magnesian layers below, with a light gray friable sandstone be- 
tween. The character of the limestone constituting the upper- 
most division is such as to merit more than a passing notice. 
Throughout its area in Iowa, and its northern outcrop in 
Illinois, it has a peculiar brecciated or concretionary structure, 
not observed elsewhere. It is made up of a mass of angular 
limestone fragments, which have become more or less firmly 
recemented together. The stratification is very irregular, though 
in some places, where the brecciated character is absent, it is 
found even enough to furnish very excellent building stone. It 
is generally hard, and often cherty, and where it forms the floor to 
the coal measures, constitues a very excellent guide to those in 
search of this useful deposit. Its cherty character makes it very 
difficult to penetrate, and so when once reached it is readily recog- 
nized. In its typical locality—at and about St. Louis, where it 
was first studied by Dr. Shumard—it is described as a fine- 
grained, compact, subcrystalline limestone, often enclosing 
numerous cherty concretions, and the layers separated by thin 
