40 GEOLOEICAL FORMATIONS 



the water level of the Mississippi river, and successively, on 

 either side, all the beds of the Hudson shales. 



North of the Missouri river, in Pike, Ealls and Marion 

 counties, the lithological characters and fossils are essentially 

 the same as in the southern part of the state. 



GIRARDEAU LIMESTONE. 



This rather well-remarked division of the lower Silurian 

 in southeastern Missouri was first differentiated by Shumard 

 in 1855, and provisionally called by him the Cape Girardeau 

 limestone, but was regarded as a member of the Upper, instead 

 of the Lower, Silurian. 



Lithologically the limestone is bluish, very compact, and 

 resembles somewhat the stones used in lithographing. It is 

 rather thinly bedded, with numerous vertical fractures or 

 joints. Fossils of peculiar types abound. Its thickness is 

 over 60 feet. 



Worthen* also recognized this formation as a distinct ho- 

 rizon, but made it the upper member of the Cincinnati group, 

 the superior part of the Lower Silurian of the region. 



UPPER SILURIAN LIMESTONES., 



The rocks which in the Mississippi valley have commonly 

 been referred to the Kiagara have not been made out satisfac- 

 torily in southeastern Missouri, and they do not appear to be 

 represented at all along the northern and western borders of 

 the Ozark uplift. 



At Louisiana, in Pike county. Mo., immediately above the 

 Hudson shales, is a bed of white oolite five feet in thickness. 

 It is overlain by a buff, dolomitic limestone, very massive, 

 and having a vertical measurement of four feet. Two miles 

 below the town this bed is ten feet thick, and still further 

 to the south is said to thicken to upward of 30 feet. Above 

 this layer are a few feet of dark-colored shales, containing 

 apparently a well-defined Devonian fauna. Then comes the 

 lithographic or Louisiana limestone. 



*Geol. Sur. niinois, Vol. Ill, p. 26. 1866. 



