EXOGYKA PONDEROSA ZONE. 31 



Of the 9 restricted species S (if Isocardia cliffwoodensis Weller is correctly identified) occur 

 in the marine invertebrate-bearing beds f orming the upper part of the Black Creek formation of 

 the Carolinas, and 1 of the 8 occurs questionably in the extreme base of the overlying Peedee 

 sand of the same region. 



Only 1 of the 9 restricted species, Eriphyla conradi (Whitfield), occurs in the Matawan 

 group of New Jersey, and this one is common to the Merchantville clay marl and the Woodbury 

 c ] a y — the two basal formations of that group. None are known in the overlying Monmouth 

 group of that State. 



CORRELATION OF THE EXOGYRA PONDEROSA ZONE. 



INVERTEBRATES. 



The Carolinas. — A study of the invertebrates of the Carolina Cretaceous deposits has shown 

 a restriction hi the stratigraphic range of the species Exogyra ponderosa in that region similar to 

 that of the same species in the eastern Gulf region. In the Carolinas the vertical ranges of 

 typical specimens of Exogyra ponderosa and Exogyra costata overlap little if any, the former 

 apparently disappearing at about the horizon where the latter makes its appearance. Exogyra 

 ponderosa occurs in the marine invertebrate-bearing beds forming the upper part of the Black 

 Creek formation. The synchroneity of these beds with at least a part of the Exogyra ponderosa 

 zone of the eastern Gulf region is clearly shown, not only by the presence of this species but by 

 that of numerous other similarly restricted species; for, as shown by the statement of ranges on 

 a preceding page, of 37 species restricted to the zone of Exogyra ponderosa in the eastern Gulf 

 region 20 occur associated with the same species in the Carolinas, and only 1 questionably iden- 

 tified form is known in the overlying Peedee sand in association with Exogyra costata — and that 

 one questionably identified form, Exogyra ponderosa var. erraticostata Stephenson, occurs only 

 in the extreme basal beds of the Peedee sand. The Exogyra ponderosa zone of the eastern Gulf 

 region is therefore with confidence correlated with a part of the Black Creek formation of the 

 Carolinas. However, the apparent absence from the marine invertebrate-bearing beds of the 

 Black Creek formation of those species regarded as characteristic of the Mortoniceras subzone 

 in the eastern Gulf region is taken to indicate that this part of the zone of Exogyra ponderosa is 

 represented in the Carolinas by a part of the Black Creek formation below the invertebrate- 

 bearing beds of that terrane. The Black Creek fauna is strictly comparable with the fauna from 

 localities on Chattahoochee River between Florence and the lower end of Roods Bend, Stewart 

 County, Ga., an air-line distance of 5 to 6 miles, and from localities in the vicinity of Union 

 Springs, Bullock County, Ala. These beds represent a part of the zone of Exogyra ponderosa 

 above the Mortoniceras subzone. 



New Jersey. — In the New Jersey Cretaceous the species Exogyra ponaerosa and Exogyra 

 costata do not overlap in their ranges, the former being known only from the MarshaUtown 

 formation of the Matawan group, and the latter being restricted to the Monmouth group. Of the 

 37 species which in the eastern Gulf region are restricted to the zone of Exogyra ponderosa, 6 are 

 common to the Matawan, and none of the 37 are known in the Monmouth (Exogyra costata 

 zone of New Jersey). All of the 6 except the species Liopistha alternata Weller, occur in the 

 marine invertebrate-bearing beds of the Black Creek formation of the Carolinas. 



It is believed, therefore, that the Matawan represents approximately the Exogyra ponderosa 

 zone of the eastern Gulf region. The occurrence of the genus Mortoniceras and the species 

 Liopistha alternata Weller in the Merchantville clay marl, which forms the basal formation of the 

 Matawan group, is taken to indicate that the Merchantville is synchronous with the Mortoni- 

 ceras subzone (lower part of zone of Exogyra ponderosa) of the eastern Gulf region, these two 

 forms being considered characteristic of that horizon. However, specimens of Mortoniceras 

 which have been referred to Mortoniceras delawarense (Morton) have been obtained from the 

 Campanien (upper Senonian) of France, 1 and specimens referred to Mortoniceras texanum 

 (Roemer) have come from the lower part of the Santonien (lower Senonian) of the same country. 2 



i Pervinquiere, L., Cephalopodes des terrains secondaires: Carte geologique de la Tunisie, Etudes de la paleontologie tunisienne. 1, 1907, pp. 

 243-245, PI. XI, figs. 21 a-b, 22. 



2 De Grossouvre, A., Les ammonites de la craie superieure: Mem. expl. Carte gfiol. de la France — Recherches sur la craie superieure, paleon- 

 tologie, pt. 2, 1896, pp. 80-83, PI. XVI, figs. 2, 3a, 3b, 4a, 4b, PI. XVII, figs, la, lb. 



