of the Devonian of Western Tennessee. 745 



thinner bedded sandy chert which weathers more readily 

 and is not well exposed. This lower portion seems to 

 vary in thickness from place to place, hut was not seen to 

 exceed 5 feet. Although so thin, this formation, with 

 both its distinctive lithology and fanna, extends over half- 

 way across the state. It was not seen north of Camden, 

 but in various exposures along Birdsong Creek and fur- 

 ther south on Lick Creek it dis conformably succeeds typ- 

 ical sections of the Birdsong shale. Where best devel- 

 oped about the town of Decaturville, it rests on the basal 

 layers of the Birdsong formation, though a full section 

 of the latter is preserved at Perryville only 6 miles to 

 the northeast. In the vicinity of Saltillo it rests in 

 places on remnants of this formation, and elsewhere on 

 the Decatur limestone, while 5 or 6 miles to the east at 

 Grandview it succeeds the Ross limestone and near Wal- 

 nut Grove at the south edge of the state it overlies the 

 Olive Hill formation. Thus far it has not been identified 

 east of the Tennessee River except in Hardin County. 



The chert is replete with fossils which are preserved 

 both as natural molds and casts and as replacements of 

 the shell in white silica. The most striking feature of 

 the fauna is the large size of many species, which exceeds 

 their norm by 25 to 50 per cent, Some of the important 

 fossils are as follows : Favosites conicus, Pleurodict- 

 yum lenticulare, Dalmanella planoconvexa, Rhipidomella 

 oblaia, Leptostrophia beckii, Leptcenisca concava, Schu- 

 chertella woolivorthana, Chonostrophia jervensis, Eato- 

 nia s'nujularis, E. medialis, Delthyris perlamellosa, 

 Meristella cf. Icevis, Anoplotheca concava, Homalonotus 

 sp. (large), and Phacops hudsonica. 



This fauna is closely allied to those of the Birdsong 

 and New Scotland formations and there are affinities 

 which equally relate it to the Becraft. Of its nineteen 

 species, twelve occur in both the New Scotland and 

 Becraft, and two others have closely related species in 

 both. Of- the remaining forms, Leptcenisca concava and 

 Phacops hudsonica are elsewhere confined to the New 

 Scotland, while Chonostrophia jervensis is limited to the 

 Becraft. The chief distinction separating this fauna 

 from that of the Birdsong or New Scotland is the absence 

 here of many characteristic species of these formations, 

 such as Eospirifer macropleura, Bilobites various, and 

 Anastrophia verneuili. On the other hand, it lacks some 



