426 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXXIV. 
Along the river bank one-half mile northeast of Perryville a large 
quarry has been opened in the Decatur limestone and a good ex- 
posure of the rocks is presented. Foerste quotes Astrwospongia 
meniscus as occurring in this quarry immediately beneath the Lin- 
den limestone. Careful collecting here shows other Niagaran fossils, 
so that there is little doubt of the correctness of the reference of this 
Jimestone to the Decatur. 
The section at Lady’s Bluff presents the Decatur limestone so well 
that the following subdivisions can be noted: 
Decatur limestone at Lady’s Bluff, Tennessee. 
i Feet. 
NG eM SORIA CLO Mates Ne tees Case nee 2 i bua atin 2 — 
Decatur limestone. : 
Mellow, Arcilla CeO US mld ES CO 1 Cee ee eee eee ec cite SEEN M TE ait 2 
Massive? White ma gieSrans 111 SS CO Cm se eee eee eee ete er eee 30 
Argillaceous, grayish limestone weathering into shale____________+_ 11 
Massive, magnesian limestone, grayish at top and yellowish toward 
PO tO Te aa TN AU TIS Re ee Pe Seite een Sean ES 20 
IOC NAANUKS IO AIE AKO) — ee i Ci MART RY Ek tds ha me Te ea Na — 
Although the three localities mentioned above afford the best sec- 
tions of the Decatur hmestone known to us, still favorable exposures 
for its study are found at numerous other places in Decatur and 
Perry counties. Southward this, as well as the underlying Lobel- 
ville formation, is usually absent, the Chattanooga black shale or 
Helderbergian strata resting upon the Bob formation. 
The following composite section of the Ordovician-Devonian strata 
of west Tennessee was prepared from a study of the numerous indi- 
vidual sections studied in this area. 
