151 



Midway Stage 37 



deposits, consist of light gray or yellowish impure limestone. 

 This is frequently eroded in a peculiar rough and irregular man- 

 ner. Silicious pebbles and flakes of mica are common ingredients 

 of the limestone. Fossils are of frequent occurrence in this for- 

 mation, but here as at Clayton, they consist only of impressions, 

 moulds and casts. They are remarkable for their resemblance to 

 or rather identity with those of the basal limestone east of 

 Middleton, Tenn., (p. 21) referred to as the Turritella rock of 

 northeast Mississippi. Among other forms may be mentioned 

 Venericardia planicosta, V. alticostata, Corbula subcompressa, Cu- 

 cullcBa probably saffordi, O. crenulimarginata (young), _ Fi^/z//^ 

 florencis, Strepsidura vtediavia, Mazzalma impressa var. orientahs, 

 Turritella tennesseensis, T. pumila, Calyptrophorus velatus var. 



A little higher up, i. e., downstream, other important species 

 are seen, such as Valuta lyroidea, Meretrix ripleyana, Leda saf- 

 fordana, Martesia dalliana, Ostrea crenulimarginata and O. pulas- 

 kensis. 



A bluish, more or less indurated, micaceous, sandy layer out- 

 cropping not far above the mouth of Sandy creek furnishes nearly 

 all the species just mentioned as well as Turritella humerosa and 

 extremely large specimens of T. mortoni. 



By far the most interesting Midway locality seen about Ft. 

 Gaines is at the landing. The Midway beds are confined to a few 

 feet of whitish crumbling limestone at the base of the bluff arid 

 are overlayed unconformably by Lignitic dark clays. As in 

 nearly all Midway limestone deposits, the shelly matter of the 

 specimens inclosed is entirely removed, and hence one is left to 

 work out the details of the various specific forms by means of 

 gutta-percha moulds. The number of new species is noteworthy; 

 the number of old ones is scarcely sufficient to permit of ac- 

 curately correlating this bed with anything heretofore described; 

 but partially on faunal and partially on stratigraphic grounds, we 

 have referred it to the upper Midway. 



Among the many specimens obtained here the following are the 

 most readily obtained and best preserved: Astarte subpontis, Gas- 

 trochcena gainesensis, G. cimitariopsis , Lithodomus gainesensis, 

 Modiola subpontis, Ostrea crenulimarginata, Chama gainesensis, 

 Venericardia sp. , Area sp. , Mitra subpontis, Volutilithes (of Midway 

 rough aspect) sp.?, Turritella mortorii yox . levicunea, Fusus tortilis, 

 Natica mediavia, Cerithium gainesensis. Moreover, a large Ceri- 

 thiimi fragment showing two internal lirations on the base of the 

 penultimate whorl and some indications of sculpturing, suggests 

 relationship with C. claytonense. Casts of Siliquaria, Area, 

 Cyprcea, Pectunculus and crab remains were also found here. 



