CRETACEOUS DEPOSITS OF THE EASTERN GULF REGION. 25 



BASAL BEDS OF THE EUTAW FORMATION. 



Sixteen species have been determined from the basal 100 or 150 feet of the Eutaw forma- 

 tion in the Chattahoochee region, and a few poorly preserved specimens, including Ostrea, 

 Gryphsea, Pecten, and Cardium, have been found at and near the base of the formation on 

 Alabama Eiver north of Montgomery. Except for these no invertebrates are known in the 

 basal beds of the Eutaw of the eastern Gulf region. 



RANGE OF THE SPECIES. 



The 16 species identified from the basal beds of the Eutaw formation in the Chattahoochee 



region are as f oUows : ' 



Fossils from basal beds of the Eutaw formation. 



Mollusca— Continued. 



Plioladomya sp. nov. d. 



Etea carolinensis Conrad . abed. 



Cypriineria depressa Conrad, a b c d. 



Baroda sp. nov. d. 



Leptosolen biplicata (Conrad), abed. 



Cymbophora lintea (Conrad), abed. 



Corbula carolinensis Conrad, bed. 



Placenticeras sp. (aff. P. guadalup;e Roemer). d. 



Mollusca: 



Nucula percrassa Conrad . a b e d. 



Perna sp. nov. c d. 



Ostrea cretacea Morton, c d. 



O. sp. nov.? (cf . undescribed species from House Bluff. 



Alabama River, Ala.), c df 

 O. sp. (aff. O. lugubris Conrad), d. 

 Exogyra upatoiensis Stephenson, d. 

 Pecten sp. nov. c d. 

 Anomia sp.nov. (also found at Snow Hill, N. C, etc.). 



bed. 



Of the 16 species listed 5 are restricted to the basal beds of the Eutaw; 10, or questionably 

 11, range upward into the Mortoniceras subzone. Of these last, 7 continue above the Mor- 

 toniceras subzone into the upper part of the Exogyra ponderosa zone; and 5 of these range on 

 upward into the Exogyra costata zone. None of the 5 restricted species are known from sur- 

 face outcrops in the Carolinas or in New Jersey. However, one of them, Exogyra upatoiensis 

 Stephenson, has been recognized recently in a well sample obtained from the depths 1,974 to 

 2,007 feet in a well boring at Charleston, S. C, and in the same sample was found an oyster 

 related to Ostrea lugubris Conrad, but differing slightly from the similarly related oyster found 

 in the basal beds of the Eutaw in the Chattahoochee region. 



CORRELATION. 



Invertebrates. — The 5 forms restricted to the basal beds of the Eutaw formation are all 

 new to science and therefore afford but little positive evidence as to the age of the terrane. 

 However, the beds in which they are found are known to occupy a position stratigrap hie ally 

 lower than any other marine invertebrate-bearing beds thus far discovered in the eastern Gulf 

 region, and for this reason, if for no other, the fauna must be regarded as the oldest of its kind 

 known in the region. The new species Exogyra upatoiensis Stephenson, which occurs in the 

 marine beds near the base of the formation, has a markedly different surface sculpture from 

 the other known species of this genus in the Atlantic and eastern Gulf Cretaceous. (See PI. XIII, 

 figs. 1-4.) The presence of this species and of the fluted oyster related to Ostrea lugubris 

 Conrad which occurs in the Eagle Ford shale of Texas may perhaps be considered paleontologic 

 evidence of the greater age of this fauna. As the conditions for the preservation of one species 

 of oyster are as favorable as they are for the preservation of any other species of the same 

 family, this new species of Exogyra and the fluted oyster would be expected to appear in the 

 collections from the overlying Tombigbee sand member if/ in this region, they had lived con- 

 temporaneously with the oyster Exogyra ponderosa Roemer, which is common in that member. 



From the range determinations as stated, the following conclusions have been deduced: 

 (1) The invertebrate fauna present in the basal beds of the Eutaw formation possesses elements 

 in common with Cretaceous faunas of higher horizons in the same region; however, in passing 



1 The range of the species is shown by the letters appended: a, Exogyra costata zone; b, Exogyra ponderosa zone above the Mortoniceras subzone; 

 c, Mortoniceras subzone: d, basal beds of Eutaw formation. 



