MISSISSIPPIAN. 403 



The strata are thus described : 



TullaTioma formation. — This formation consists chiefly of siliceous shales and limestones, but 

 the lowest member is a calcareous shale, generally a grayish green or pale blue but occasionally 

 dark, varying from nothing to perhaps 30 feet in thickness. * * * -phe fossils, though 

 chiefly of undescribed species of Ostracoda, indicate very early Mississippian age. * * * 



A strongly sihceous and argillaceous limestone that weathers into a cherty, shalelike mate- 

 rial occurs stratigraphically above the calcareous shale but usually constitutes the ordinary 

 base of the formation. Similar strata, in one place more shaly, in another more calcareous, 

 and generally with heavier chert, continue to the top of the formation, which has a maximum 

 thickness of aUout 250 feet. Usually it is much less, especially in the southeastern quarter of 

 the quadrangle. * * * 



Excepting in the basal shales, specifically recognizable fossils are extremely few in this 

 formation. Here and there the heavier chert blocks contain large crinoid stems in abundance, 

 and occasionally a brachiopod cast, indicating the Burlington or Keokuk horizon of Iowa and 

 Illinois. 



St. Louis limestone. — This, the latest or youngest formation exposed in the quadrangle, 

 consists in the main of a thick bed of limestone, gray to blue in color, and associated with con- 

 siderable chert. * * * Ti^g fossils are mostly small and consist mainly of Bryozoa and 

 brachiopods more or less characteristic of the "Warsaw horizons" of Illinois, Indiana, and 

 Kentucky, which have been referred to various ages. Above these heavy layers come the 

 more characteristic St. Louis fossils, like Melonites and Lonsdaleia, or as the latter is generally 

 called, Liihostrotion canadense. 



In 1894 the Alabama section of the Mississippian was thus classified by Smith^^® : 



Mountain limestone: 



(a) Bangor limestone and Hartselle sandstone. 



(6) Oxmoor shale and sandstone. 

 (Chester.) 

 Fort Payne: 



(a) Tuscumbia (St. Louis). 



(6) Lauderdale (Keokuk, etc.). 



This classification has since been revised and modified. The latest statement 

 is by Butts/"^" as follows: 



Overlying the Devonian black shale unconformably are rocks of Mississippian or lower 

 Carboniferous age. At the base of the Mississippian rocks, throughout the whole region, is 

 the Fort Payne chert; this is succeeded in Brown and Murphrees valleys by the Bangor lime- 

 stone, with the included Hartselle sandstone member, and by an overlying shale which is cor- 

 related on stratigraphic and lithologic grounds with the Pennington shale to the north. At 

 the southern end and along the east side of Blount Mountain, and along the east side of Shades 

 Valley, the Pennington shale is overlain by shales and sandstones to which the name Parkwood 

 formation is here given. South of Boyles Gap in Opossum Valley and south of Oxmoor in 

 Shades Valley the Bangor limestone runs out and is replaced by black and gray shales similar 

 to the Floyd shale to the northeast. Because of its stratigraphic position and lithologic simi- 

 larity this shale wiU be called Floyd shale in this report. South of Boyles Gap and Oxmoor, 

 therefore, the Mississippian rocks above the Fort Payne chert consist of the Floyd shale 

 (including the Hartselle sandstone, which persists after the thinning out of the Bangor limestone 

 and thus locally becomes a member of the Floyd shale) and the Parkwood formation above the 

 Floyd. The Floyd shale is thus the equivalent of the Bangor limestone and the Pennington 

 shale. In reports of the Alabama Geological Survey the Floyd shale and the rocks comprising 

 the Parkwood formation have been treated together as the "Oxmoor or shale and sandstone 

 phase" of the upper part of the lower Carboniferous rocks, and the Bangor limestone has been 

 called the "Bangor or limestone phase" of the same rocks, the two phases being regarded as 

 contemporaneous . 



