716 C. 0. Dunbar — Stratigraphy and Correlation 



of the most distinctive forms of the Becraft, such as 

 Aspidocrinus scutelliformis, Rhipidomella assimilis, and 

 Spirifer concinnus. The faunal evidence is, therefore, 

 not very conclusive, but it is not out of harmony with the 

 assignment of this formation to early Becraft time. 

 This reference of the formation, however, is based rather 

 on its stratigraphic position. The distinct unconformity 

 with which the formation overlaps the Birds ong shale 

 indicates a considerable time break between it and the 

 New Scotland equivalent, and since a thick section of the 

 latter is already represented in the Birds ong formation, 

 the distinctly younger Decaturville chert seems to be 

 best referred to the earliest Becraft. The Becraft sea 

 probably entered the Mississippi basin by the same route 

 as that of the New Scotland, since it is present in south- 

 ern Illinois, where Savage (1908) has reported such char- 

 acteristic Becraft fossils in the upper part of the Bailey 

 limestone as Aspidocrinus scutelliformis and Spirifer 

 concinnus, associated with Oriskania condoni (?) and 0. 

 sinuata n. var. 



Oriskany Group 



The upper Oriskany, with its characteristic fauna of 

 large species, is typically developed in the Appalachian 

 trough extending from Gaspe to southern Virginia, but 

 previous to 1913 it was believed that this sea had never 

 attained the Mississippi basin. In that year, however, 

 "Weller (1914) discovered a very small occurrence of 

 white limestone in eastern Missouri carrying this distinc- 

 tive fauna. It is one of the chief contributions of the 

 present study to record an extensive development of the 

 typical upper Oriskany along the Tennessee valley, where 

 it attains a thickness of over 50 feet and is exposed in 

 numerous places for a distance of more than 75 miles. It 

 unconformably overlies the Linden group and is in turn 

 separated by local unconformities from the succeeding 

 Camden chert. The Oriskany equivalents are here 

 divided into the lower Quail and the higher Harri- 

 man formations. The former name is applied to the 

 basal siliceous limestone, and the latter to the much 

 thicker and more extensively distributed superimposed 

 novaculite. 



Quail limestone. — This thin limestone formation is 

 confined to the southern part of the state, having a 



