744 C. 0. Dunbar — Stratigraphy and Correlation 



The intimate relationship of this fauna to that of the 

 Eoss member of the Olive Hill formation is shown in 

 the fact that fifty-one out of fifty-eight species from the 

 latter pass into the Birdsong shale. On the contrary, 

 there is great deployment of Camarocrinus in the Ross, 

 as in the Eockhouse shale, whereas these fossils are gen- 

 erally not common in the Birdsong formation, and nei- 

 ther the distinctive Scyphocrinus pratteni nor its huge 

 bulb has been seen in the latter formation. At the same 

 time, thirty-five species appear in the Birdsong that have 

 not been found in the Eoss. The most importance is 

 attached to Eospirifer macropleura, which is always to 

 be found in the Birdsong and never in the Olive Hill. 

 Equally characteristic species of the former formation, 

 such as Eatonia tennesseensis, Camarotoechia bialveata, 

 Dalmanella perelegans, and Bahnanites retusus, are 

 also lacking in the Olive Hill. The absence of these 

 species from the Eoss and Pyburn limestones may not be 

 attributed to the control of the sediments, since they are 

 known to occur elsewhere in impure cherty limestones. 

 To this fauna evidence for the distinctness of the Bird- 

 song shale from the Olive Hill formation should be added 

 that of the general field relations. To correlate the Bird- 

 song shale with the Eoss limestone would demand a very 

 abrupt faunal and lithologic change between Perryville 

 and Grandview, though each formation maintains its own 

 characters with uniformity for many miles from these 

 localities. But the existence of any such transition is 

 negated by the outlier of the Birdsong formation at Sal- 

 tillo, which is as far south as Grandview. This being 

 true, the erosion of the Eoss limestone from the vicinity 

 of Saltillo must have preceded the deposition of the 

 Birdsong shale, and this fact, as well as the faunal evi- 

 dence, precluded the correlation of the latter with either 

 of the members of the Olive Hill formation. 



Becaturville chert. — This thin formation is the highest 

 member of the Linden group and unconformably overlies 

 all of the preceding formations. It is well developed in 

 the vicinity of Decaturville, from which place it takes its 

 name. The most distinctive and widespread part of the 

 formation is a very porous and extremely fossiliferous 

 gray or slate-colored chert, which on the surface is 

 stained with iron rust, and which forms a heavy layer 

 from a few inches to over a foot thick. Beneath this is 



