of the Devonian of Western Tennessee. 751 



formation is unconformable overlain by the much 

 younger Chattanooga shale. 



The Camden chert attains a total exposed thickness of 

 164 feet along Cypress Creek southeast of Camden, and 

 if the layers exposed at the "whirl" on the Buffalo River 

 be added, it has a total of about 200 feet. The log of the 

 city well at Camden shows a thickness of 275 feet, which 

 is to be divided between this and the Harriman chert. It 

 is well developed from Big Sandy northward along the 

 course of the Big Sandy River, and it also extends south 

 of Camden along the valley of Birdsong Creek, but it 

 seems not to extend as far south as Perryville and Par- 

 sons, the chert there exposed being referable entirely to 

 the Harriman formation. While thicker in the more 

 western sections, it appears to thin out by overlap east- 

 ward, only the succeeding Pegram limestone reaching as 

 far eastward as Nashville, and in most sections its thick- 

 ness is greatly reduced by later erosion. The formation 

 doubtless continues under cover into southern Illinois, 

 where it has a maximum thickness of 237 feet and is 

 known as the Clear Creek chert. 



The magnitude of the unconformity which separates 

 the Camden chert from the Harriman chert below is 

 shown by the circumstance that the latter has a thickness 

 of 55 feet on the lower course of Big Sandy River, but is 

 entirely absent by erosion on Rushing Creek about 7 miles 

 south of Big Sandy, where the Camden chert rests 

 directly on the Birdsong shale. Just south of Camden, 

 the Harriman chert is again well developed beneath the 

 Camden, but here its thickness can not be determined. 

 The sharpness of the faunal break still further empha- 

 sizes the importance of the hiatus between these forma- 

 tions. 



The fossils of the Camden chert are preserved as sharp 

 natural molds and casts of both the exterior and interior, 

 showing details of sculpture and internal characters in 

 unusual perfection. As a whole the formation is abun- 

 dantly f ossilif erous, but some layers are relatively barren 

 while others are replete with fossils. Among the more 

 characteristic species of this formation are: Stroplieo- 

 donta cf. hemispherica, Scliuchertella pandora, Eodevo- 

 naria arcuata, Chonetes Jiudsonicus mut. camdenensis 

 n. mut., Anoplia nucleata, Chonostropliia reversa, Cen- 

 tronella glansfagea, Amphigenia curta, Orishania con- 



