SILURIAN-DEVONIAN UNCONFORMITY 413 



is white limestone 2 feet thick, which probably belongs to the base of the 

 Laurel. The Black shale lies immediatel}^ above. About If miles far- 

 ther eastward, at a spring in Terrel hollow (locality 21), the Black shale 

 rests on Clinton limestone 18 feet thick. At Foggs post office (locality 

 20), 12^ miles southwest of Tottys Bend post-office, 3 J miles northeast of 

 the last locality, the Black shale rests on very hard white Clinton lime- 

 stone 5 feet thick and contains chert nodules. 



While at Centerville (locality 25) the Black shale rests on the Waldron 

 shale, two miles south of Centerville, in the hollow near Sam Turner's 

 log house (locality 24), a short distance north of Mrs Isabella Wiss' 

 home, Black shale rests on only 8 feet of Clinton limestone containing 

 layers of cherty nodules. A short distance southeastward, at the Dean 

 phosphate quarry, the Black shale rests on the Ordovician limestone. 



Moreover, while above the spring in the Tan Yard hollow (locality 22) 

 the Black shale rests on rock believed to belong to the base of the Laurel 

 limestone, a mile and a half farther southward, about 225 feet north of 

 the spring north of the home of Mrs Rebecca C. Orman (locality 23), the 

 Clinton beneath the Black shale has a thickness of only 9i feet. It con- 

 tains chert nodules. At Swan bluff, farther south, the Black shale rests 

 on the Ordovician. 



At the Tennessee Mines, 41 miles south of Swan bluff, the Black shale 

 rests on the Ordovician. A short distance farther south, where the road 

 going downhill crosses a little stream (locality 28), the Black shale rests 

 on several chert layers, which have a thickness of 2i feet. OnW the 

 chert is preserved, the intermediate limestone having decayed and dis- 

 appeared. Beneath is cross-bedded Ordovician limestone. On the other 

 side of Swan creek, on the road leading from Tennessee Mines across the 

 creek and then down the east side of the valley, is a bluff (locality 29) 

 of massive white limestone about 11 feet high, believed to belong to the 

 Clinton. As is usual along the headwaters of Swan creek, the lower and 

 middle parts of the Clinton are heavily bedded and free from cnert. 

 While chert occurs at various localities in the lower part of the Clinton, 

 as already noted, this is rather exceptional. The bluff mentioned is on 

 the W. D. Aydlott property, about a quarter of a mile south of the road 

 crossing the creek east of the mines. The Black shale is immediately 

 above the Clinton, but the base of the latter is not seen. About a mile 

 north of the Lewis County line, on the east side of the creek, west of the 

 home of Anderson Morris (locality 30), the Black shale rests on 26 feet 

 of Clinton limestone. The base of the Clinton is not seen. The upper 

 2J feet of the exposure consist of fossiliferous cherty beds, below which 

 are 6^ feet of limestone with the chert in the form 6f laj'-ers of nodules. 

 A layer containing Heliolites rather abundantly occurs immediately be- 



