310 
GRASSY BLACK SHALE 
tion was to regard the entire shale section between the Callaway 
limestone and the Chouteau limestone as a distinct and compact 
lithologic unit, Devonic in age, perhaps, but having intercalated 
the lens of Louisiana limestone. This conclusion was based part¬ 
ly, perhaps largely upon faunal grounds, and especially upon the 
character of the Gomphoceras fauna then newly found well up 
in the section at Burlington, in what is doubtless a horizon of the 
Saverton shale, there merging without evidence of break with the 
Hannibal shale. Afterwards the fauna was noted by Weller.^* 
It 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 Doctor Calvin to Professor Weller for critical 
examination. As one of the results Weller was led to correlate 
the lithographic limestone (bed 4) of the Chouteau formation 
at Burlington, with the Louisiana limestone of Missouri, and to 
regard the fossils of the shale as constituting the oldest Kinder- 
hook fauna. 
Assuming the Grassy shale to be a northward extension of the 
southern Chattanooga black shale it may be accepted that the 
shallow, northward advancing seas in which it was deposited 
finally encountered the northwestern waters in which still swarmed 
Devonic types. The blue shales which preserve remains of the 
latter are known as the Lime Creek shales in northern Iowa, 
and the Snyder shales in central Missouri. The Saverton green 
shale which immediately overlies the Grassy black shale with its 
first Carbonic fauna, appears to have been laid down in seas 
which marked a slight advance from the north. Whether or not 
the Saverton fauna is really a purely Devonic facies hanging over 
from a previous time, or whether it is really identical with the 
Snyder fauna is yet an undetermined question. The fossil as¬ 
semblages now known in them are yet too meager for final de¬ 
termination ; but present evidence points strongly in this direction. 
24 Iowa Geol. Surv., Vol. X, p. 69, 1900. 
25 Ibid., Vol. Ill, p. 433, 1895. 
26 Ibid., Vol. X, p. 70, 1900. 
27 As a formational title Snyder wa slong usel as a field name by the Missouri 
Geological Survey. It was a name appearing upon the cadastral maps of Callaway 
county; and was widely known by the dwellers around Fulton. Its first appearance in 
print may have been by Galleher in 1900; but it was also defined clearly by Keyes 
in 1902. Between tha date and the time when Greger proposed the title Craghead 
from the same section the term Snyder was used in a number of publications. Greger’s 
name is therefore a synonym. 
