THE BARITE DEPOSITS OF MISSOURI 51 



ade formation in the Ordovician system. The St. Peter sand- 

 stone is Ordovician in age. 



The St. Peter formation and the Mississippian and the 

 Pennsylvanian systems are not very widespread in the district, 

 their outcrops being confined mainly to the northern part. 



A httle barite has been reported from the Burlington lime- 

 stone, but the deposits are of minor importance. The barite dig- 

 gings that are of importance are associated with the Gasconade, 

 Roubidoux, and Jefferson City formations. 



The rocks are all essentially horizontal, there being few 

 notable departures from this position. Such simple structure is 

 known to exist over a large part of the Ozark Plateau, broken 

 here and there by slight folds or a few faults. There are some 

 faults of 150 feet throw in the Gasconade formation, but only 

 very small or broad and gentle folds are known. 



Since the barite is mainly in the Gasconade, Roubidoux, 

 and Jefferson City formations the general characteristics of 

 these formations only are given. 



The Gasconade formation. — The Gasconade formation, 240 

 feet to 290 feet thick, is composed of beds of (1) cherty and 

 non-cherty dolomite; (2) beds of chert; and (3) occasional beds 

 of sandstone. Dolomite greatly predominates. The lithological 

 features are uniform over a large part of the area, the principal 

 variation being in the sandstone which occurs as a rule in lenses. 

 The dolomite is crystalline, mostly gray in color, and with mas- 

 sive beds alternating with thin ones. As a rule thin beds are 

 finer in grain than the massive ones. The chert is in nodules, 

 layers, and small masses, and as beds, some of which are several 

 feet thick. A few of these beds are brecciated. The chert, which 

 is disseminated, always occurs along certain beds in chert hori- 

 zons. White is the predominating color, but some of it is also 

 grayish-yellow, bluish- white, and even black (flint). Some 

 oolitic chert occurs, especially in Miller County. 



The sandstone consists of well-rounded grains of quartz of 

 medium size, such sandstones being principally in Miller County. 

 Aside from the Gunter sandstone, the sandstone lenses are rarely 

 more than two feet thick. The Gunter member at the base of 

 the Gasconade ranges from 5 to 35 feet thick. It is composed of 



