MISSTSSIPPIAN CHERT OF ST. LOUIS AREA 369 
of note, although very possibly nothing more than a coincidence, 
that much chert is found in the lower Carboniferous limestones of 
England, Ireland, and Belgium. 
AGE OF CHERT 
In age the chert of the Mississippian of the St. Louis seems 
without doubt to lie between the early Pennsylvanian and the time 
of formation of the chert-bearing limestones. The evidence of the 
pre-Pennsylvanian age of the chert lies in the presence of the Mis- 
sissippian chert as clastic fragments in the base of the Pennsylva- 
nian. In a Missouri-Pacific railroad cut between Kirkwood and 
Barrett’s Station, St. Louis County, Missouri, and also in a Frisco 
railroad cut a half-mile east of Meramec Highlands, clastic chert 
carrying Lithostrotion proliferens and Spirifer Keokuk and showing 
predepositional weathering is to be found in abundance at the base 
of the Pennsylvanian shales. In Miller County, Missouri, clastic 
chert from the Burlington limestone is reported as being present in 
the Graydon sandstones and the Coal Measures shales. In the 
Joplin district likewise clastic Burlington chert is reported as lying 
at the base of the Pennsylvanian. 
The evidences of the formation of the chert later than the forma- 
tion of the containing limestone are several. The replacement of 
fossils has been cited and probably in some cases correctly so. 
Although the fossils in the great number of cases have not been 
replaced, the replacement of the fossils, especially the larger ones, 
when studied in their sections under a microscope seems, partly at 
least, surely to have taken place after the formation of the chert. 
The retention in the chert of the markings of the limestone, includ- 
ing the grain, stratification, styolithes, and fossiliferous character, 
is valid evidence of the secondary character of the chert. The 
mottling of the chert in very many cases accurately reproduces the 
appearance of the granular character of the limestone. The strati- 
fication markings and the variation in grain and fossil content in the 
different layers can in many cases be traced into or across the chert. 
The arching of the stratification and the faulting and slickensiding 
at the contacts of the nodules are also evidences of the secondary 
character of the chert. The stratification of the limestone in which 
