No. 1621. 
Devonian. 
| Period. 
Silurian (Niagaran). 
LATE NIAGARAN STRATA—PATE AND BASSLER. 427 
Composite section of Ordovician-Devonian rocks of west Tennessee. 
Thickness. 
= 
Columnar 
section, 
Description. 
10’ 
35/ + 
Chattanooga black shale. 
Black, fissile, carbonaceous shale, often with a band of phosphatic 
material at the base and a layer of phosphate nodules at the top. 
~Hardin sandstone member. 
Sandy shales and sandstones containing fish remains. 
| Camden chert. 
Siliceous limestone weathering into beds of angular chert fragments. 
Fossils of Lower Oriskany age often extremely abundant. 
|Linden formation. 
Massive crinoidal limestone in lower half and blue shales and thin 
| limestones in upper part. Camarocrinus saffordi is the most conspic- 
uous fossil of the lower limestone (Ross bed of Foerste). The upper 
| shaly beds (Pyburn beds of Foerste) are crowded with fossils of New 
Scotland age, Strratopora issa, Favosites conicus, Callopora perelegans, 
| Eridotrypa corticosa, and Lioclema cellulosum being particularly 
abundant. 
Decatur limestone. 
Massive, white, coarsely crystalline, crinoidal and magnesian lime 
stone becoming yellow and slightly shaly at the top. 
Lobelville formation. 
Coral zone (45/). 
Yellow clays and thin clayey limestone crowded with corals. 
Several species of Favosites, Heliolites, Thecia, Cystiphyllum, 
Halysites, aud Plasmopora are very abundant. 
Bryozoan zone (81’). 
White to blue shales holding a few corals and many bryozoa in 
the upper part; red to purple shalesand argillaceous limestone 
with the same fauna making up the lower division. 
