62 IOWA ACADEMY OF SCIENCES. 



occupy the same stratigraphical position, and this only a very 

 careful study will determine. The shales as brought up to the 

 surface by the disturbance which was somewhat relieved by 

 the great fault, are well exposed on Buffalo and many of the 

 other creeks in the vicinity of Louisiana, where over 40 feet 

 are shown above the water level of the Mississippi river. 

 The fossils found in these shales have been listed in another 

 place. The shales are regarded as forming the uppermost 

 member of the Ordovician of this region. 



Noix Oulite. — Immediately above the Ordovician shales at 

 Louisiana and in the vicinity, is a very white, massive oolite, 

 containing numerous fossils and having a thickness of four to 

 seven feet and upwards. Its areal distribution is over 100 

 square miles. It is best exposed, perhaps, in the immediate 

 neighborhood of Louisiana in the- valley of Noix creek and 

 along the bluffs of the Mississippi river. Prom this locality 

 its extends westward and southward, reaching the northern 

 part of Lincoln county, Missouri, where it occurs in isolated 

 areas in the tops of the hills. It also crops out below Louis- 

 iana in the east bluffs of the Mississippi, near Hamburg in Cal- 

 houn county, Illinois. 



The character and variety of the fossils contained is indicated 

 in the list of fossils given recently in a previous volume of the 

 Academy's proceedings. 



Boioling Green Limestone. — Closely associated with the oolite 

 on Noix creek, is a buff, massive, magnesian limestone. At 

 Louisiana it is only four to five feet thick, but this measurement 

 rapidly increases westward and south westward to twenty -five 

 or thirty feet. Near Bowling Green, twelve miles southwest 

 of Louisiana, it is well displayed to its full thickness, and at 

 the same time shows all its other distinctive characters. In 

 Calhoun county, Illinois, it yields a characteristic fauna, and 

 attains a maximum thickness of thirty feet. The Noix oolite 

 and the Bowling Green limestone together may be regarded 

 approximately as equivalent to the so-called Niagara of the 

 upper Mississippi basin, and is the only representative of the 

 whole Silurian, or upper Silurian of the earlier geologists. 



Callaway? Limestone. — On the north margin of the Ozark 

 uplift the lower Devonian beds, that is, the layers lying between 

 the Silurian limestone (Bowling Green) and the Louisiana 

 limestone, are represented by highly fossiliferous strata, lime- 

 stone below and shale above. In central Missouri, in Callaway 



