IOWA ACADEMY OF SCIENCE 
153 
NETHER DELIMITATION OF OUR CARBONIC ROCKS. 
By Charles Keyes. 
The exact stratigraphic relations of, and the exact boundary line between, the 
latest Devonic formations and the earliest Carbonic rocks of the Mississippi 
valley north of the Missouri river have long remained some of the unsolved 
geographic problems. That the question should stand today much as it did 60 
years ago is due chiefly to the circumstance that although three state geological 
surveys have repeatedly attacked it all the necessary facts were not available 
in any one state alone. No observer seems to have had the opportunity to 
make critical investigations in all three of the states or to have gone over all of 
the ground between the mouth of the Missouri river and the Minnesota line. 
Recently during the progress of certain investigations for city water supplies 
in Iowa, Missouri and Illinois, it became necessary to make some rather nice 
calculations on the thickness and extent of sundry geologic formations. In 
the course of this work a number of facts were disclosed bearing directly 
upon the vexed problems mentioned. There are given us for the first time • 
definite data upon the actual stratigraphic relations existing between the 
rocks of the two distinct geologic ages. 
The general geologic section of the Devono-Carbonic rocks of southeastern 
Iowa and northeastern Missouri is as follows: 
Carbonic : 
General Geologic Section. 
Burlington limestone Feet — 
Chouteau limestone 10 
Hannibal shales 75 
Louisiana limestone 50 
Saverton (blue) shales* 50 
Grassy (black) shales 40 
Devonic : 
UNCONFORMITY. 
Lime Creek (blue) shales ...125 
Cedar limestone — 
The stratigraphic relations of the several terranes are best shown in cross- 
section as they are plotted along the line of the Mississippi river from Louisiana, 
Missouri, to Muscatine, Iowa. (Figure 1.) 
Detailed vertical sections I have given in another placet. At this time the 
shales lying at the base of the Louisiana limestone were little considered, since 
at the town of Louisiana they were only two feet thick and the northern 
'•■This name is the local one usually applied the blue shales lying between the 
grassy black shales and the Louisiana limestones as well exposed at Saverton station 
in Ralls county, Missouri. The formation probably attains a maximum thickness of 
at least 75 feet. 
fBull. G-hol. Soc. America, Vol. Ill, p. 283, 1892. 
