IBS C. 0. Dunbar — Stratigraphy and Correlation 



sion of the PI euro diet yum, which is mature in the three- 

 celled stage, indicate for the formation a place very early 

 in the Devonian. This inference is further supported by 

 the thick development of overlying strata of Coeymans 

 and New Scotland age. The Blockhouse shale is, there- 

 fore, believed to represent a part of the Keyser formation 

 at the known base of the Lower Devonian, although it 

 belongs to a different basin and hence shows but slight 

 faunal relation to the Keyser. 



Olive Hill formation. — The Olive Hill formation suc- 

 ceeds the Rockhouse shale and further northward over- 

 lies the Decatur limestone, but, like the preceding forma- 

 tion, it is confined to the southern part of the state. The 

 present outcrops occur in Hardin County, Tennessee, and 

 adjacent portions of Mississippi and Alabama. At about 

 the northern edge of Hardin County, it has been rapidly 

 bevelled off by interf ormation erosion, while to the south- 

 ward it goes permanently below drainage, with unreduced 

 thickness. Lithologically it is a complex formation. 

 The best exposure and the one from which it takes its 

 name is clearly shown in the bluff on Indian Creek at 

 Olive Hill, where it is fully 150 feet thick and consists of 

 three distinct lithologic units. These are, in descending 

 order, the Flat Gap, the Bear Branch, and the Ross lime- 

 stone members. 



The Flat Gap member is a heavy-bedded, coarsely 

 crystalline or granular limestone of white or pinkish 

 color, and is very sparingly fossiliferous. Toward the 

 top Rhipidomella oblata and Spirifer cycloptera are com- 

 mon, and Delthyris perlamellosa and Dalmanites pleu- 

 roptyx are quite rare. Colonies of massive bryozoa and 

 large pieces of crinoid stems complete the fauna. 



The Bear Branch member consists of more impure, 

 coarse-grained limestone in which there is a considerable 

 quantity of oolitic hematite. The latter varies greatly 

 in richness, and may be disseminated through the lime- 

 stone, giving the whole a deep reddish color, or may be 

 concentrated into richer bands of ore separated by layers 

 of limestone. The member takes its name from an 

 exposure on Bear Branch about 2 miles southeast of Olive 

 Hill, where it forms a low bluff showing a thickness of 20 

 feet of low-grade ore (protore), analyzing on an average 

 from 20 to 25 per cent Fe and much resembling the^ Clin- 

 ton iron-ore. So far as the writer is aware, this is the 



