IOWA ACADEMY OF SCIENCE 
155 
section of the Upper Mississippi region. At Louisiana these shales recline 
directly upon Silurian limestones. A few miles away they lie immediately 
upon the Callaway (Devonic) limestone. Farther on the Lime Creek shales 
are found immediately beneath. At their base, therefore, a marked unconformity 
exists, which is also well displayed at the north above Muscatine. 
The present correlation of the Grassy black shales seems to set at rest several 
moot questions. They doubtless represent the Chattanooga black shales which 
in the south constitute, according to Schuchert*, the base of the Mississippian 
section. 
They are not to be regarded as Devonic in age, as suggested by Uddent. They 
are not a local development of uncertain affinities as stated by Calvin!; nor 
do they underlie the Lime Creek shales as indicated in his general geologic 
section of Iowa§. It appears that Owen and Norwood jl, in drawing the line of 
separation of the Devonic and Carbonic strata in the Mississippi valley at 
the black shale, displayed phenomenally keen insight into the real geologic suc- 
cession in the region. 
Particularly noteworthy, the Burlington section remains. When discussing 
the Devonic Interval in Missouri** I was inclined to regard the entire shale- 
section between the Cedar limestone and the Chouteau limestone as a distinct 
unit, Devonic in age, and having intercalculated the lens of Louisiana lime- 
stone. This conclusion was based largely upon faunal grounds and especially 
upon the Gomphoceras fauna, then newly found high up in the section at Bur- 
lington, and afterwards especially noted by Wellertt- This fauna was discovered 
by me at the time that the report on Des Moines county was being printed!!; 
and six years later the fossils were turned over by Dr. Calvin to Professor 
Weller for critical examination. As a result, Weller was led to correlate§§ the 
lithographic limestone (bed 4) of the Chouteau formation, at Burlington, with, 
the Louisiana limestone at the typical locality, and to regard the fossils of the 
shales as constituting the oldest Kinderhook fauna. 
Stratigraphically there seems to be no doubt whatever that Bed 4 at Bur- 
lington cannot possibly be the continuation of the Louisiana limesone. Yet, 
there is really no serious faunal discrepancy in Weller’s determinations. That 
the older fauna — a fauna of marked Devonic aspects — should occur at a strati- 
graphic horizon higher than that of the Louisiana limestone is not remarkable. 
It is easily explained. At Burlington the shale succession from the Grassy 
shales to the Chouteau limestone is uninterrupted; at Louisiana a thick lime- 
stone divides the shales. In the north the fauna of the Grassy black shales 
continued upward unbroken. The Gomphoceras fauna from the shales 40 feet 
below the Burlington limestone at Burlington is probably the characteristic 
fauna of the Hannibal shales, although the latter at the typical locality have 
thus far proved unfossiliferous. 
*Bull. Geol. Soc. America, Vol. XX, p. 548, 1910. 
tlowa Geol. Surv., Vol. IX, p. 301, 1899. 
Uournal of Geology, Vol. XIV, p. 572, 1906. 
§Iowa Geol. Surv., Vol. XVII, p. 192, 1907. 
II Researches on the Protozoic and Carboniferous Rocks of Central Kentucky during 
the year 1846, 1847. 
**Bull. Geol. Soc. America, Vol, XIII, p. 267, 1902. 
t+Iowa Geol. Surv., Vol. X, p. 69, 1900. 
Ulbid., Vol. Ill, p. 433, 1895. 
§§Ibid., Vol. X, p. 70, 1900. 
