134 
SILURIC FORMATIONS IN MISSOURI 
hand it is considered as being the attenuated southern extension 
of an important rock-series of Iowa and the upper Mississippi 
valley.® 
The Bowling Green formation is not widely understood; and 
its features are often misinterpreted. The lower part of the 
bui¥-brown limestones, or dolomites, are commonly regarded as 
belonging to the typical Bowling Green section. This is by no 
means the case. The type-section near the town of Bowling 
Green displays at the base about a foot of yellow fossiliferous 
beds which ordinarily appear as part of the main body of dolo¬ 
mite. When the geographic title was first proposed for the for¬ 
mation these bottom layers were not considered.^ A lower buff 
limestone was noted at Gyrene, and other places south of the 
original locality, and it was regarded as the equivalent of the 
Noix oolite. To these basal beds Savage ® afterwards gave the 
name Gyrene member. 
In many of the Bowling Green sections in southern Pike 
county and in the northern portion of Lincoln county the Sexton 
member is commonly overlooked; and the entire section called 
the Bowling Green member. 
Sexton limestone, as it occurs in Pike Gounty, Missouri, consists 
of only a few feet of massive, gray beds which were recently 
designated by Savage ® the Sexton formation. Farther to the 
south in Lincoln county, this formation, with a thickness of nearly 
twenty feet, is recognized, although not by name, by W. B. 
Potter.^® Number 4 of the section given, appears to be the Sexton 
limestone, assigned a Devonic age. The basal layers constitute 
the Pentamerella zone. 
The Sexton limestone is the upper body of the massive forma¬ 
tion called by A. H. Worthen the Niagara limestone, as exposed 
on the Mississippi river, in Galhoun county, Illinois. Since it 
there attains a thickness of more than 50 feet it is probable that 
its vertical measurement in Lincoln county, Missouri, is very 
much greater than has been heretofore reported. 
Marking the base of the Sexton limestone appears to be a well- 
6 Missouri Geol. Surv., Vol. IV, p. 30, 1894; also. Am. Jour. Sci., (4), Vol. 
XXXVII, p. 254, 1914. 
7 Proc. Iowa Acad. Sci., Vol. V, p. 60, 1898. 
8 Am. Jour. Sci., (4), Vol. XXVIII, p. 509, 1909. 
9 Am. Jour. Aci., (4), Vol. XXVIII, p. 509, 1909. 
10 Missouri Geol. Surv., Iron Ores and Coals, Pt. ii, p. 244, 1873. 
— 11 Illinois Geol. Surv., Vol. IV, p. 6, 1870. 
