32 



CRETACEOUS DEPOSITS OF THE EASTERN GULF REGION. 



It is not certain that these forms have been correctly identified with the American species, but 

 in view of the higher range of the genus in the European Cretaceous than in the supposed corre- 

 sponding deposits in America it is best not to rely too strongly on tins evidence in attempting to 

 correlate exactly the eastern Gulf and New Jersey Cretaceous deposits. The remainder of the 

 Matawan group, including in ascending order the Woodbury clay, the Englishtown sand, the 

 Marshalltown formation, and the Wenonah sand, is believed to correspond to the part of the 

 zone of Exogyra ponderosa between the Mortoniceras subzone and the base of the zone of Exogyra 

 costata of the eastern Gulf region. 



Texas. — The Mortoniceras subzone contains a number of mollusca known to be common to 

 the Austin chalk of Texas and particularly to the upper part of that formation. These are as 



follows : 



Fossils common to Mortoniceras subzone and Austin chalk. 



Ostrea diluviana Linnaeus. 

 Gryphaea aucella Roemer. 

 Exogyra ponderosa Roemer. 

 Radiolites austinensis Roemer. 



Baculites anceps Lamarck? 

 B. asper Morton. 

 Placenticeras planum Hyatt. 

 P. guadalupae (Roemer). 



In the eastern Gulf region 4 of the species named in the list — Gryphsea aucella Roemer, Exo- 

 gyra ponderosa Roemer, Radiolites austinensis Roemer, and Baculites asper Morton — are known 

 to range above the Mortoniceras subzone into the basal beds of the overlying Selma chalk. The 

 remainder appear to be restricted to the Mortoniceras subzone. In Texas 1 of the listed species, 

 Exogyra, ponderosa Roemer, is known to range above the Austin chalk into the Taylor marl, and 

 it is probable that future studies will reveal a higher range for some of the other species. Mor- 

 toniceras sp. (aff . M. texanum Roemer) of the eastern Gulf region is probably represented in the 

 Austin chalk, but this has not been certainly verified. It seems probable that the Mortoniceras 

 subzone of the eastern Gulf region will be found to be synchronous with a part of the Austin 

 chalk. 



This correlation has already been .suggested by Stanton. 1 Referring to the occurrence of 

 Placenticeras syrtalt var. hahi Hyatt in Greene County, Ala., he says hi a footnote quotation 

 by Hyatt: "Age: This specimen is probably from the Eutaw beds, which are probably very 

 near the horizon of Placenticeras guadalupae [Austin chalk] hi Texas." Stanton, 2 hi discussing 

 the distribution of faunas of Colorado age, with which the Austin chalk is correlated, also states: 



No marine faunas of Colorado age are known in the Atlantic and Gulf borders east of western Arkansas, unless 

 possibly the imperfectly known fauna of the Eutaw or '"Tombigbee" sand of Mississippi belongs to its latest phase. 



However, so little is known of the fauna of the overlying Taylor marl that an attempt at exact 

 correlation would be premature, ('specially as investigations are now being conducted in that 

 region . 



VERTEBRATES. 



Teeth and fragmental bones of vertebrates occur in places in the Exogyra ponderosa zone 

 in the eastern Gulf region The following species of fish have been identified: 



Fish remains from Exogyra ponderosa zone. 



Enchodus ? petrosus Cope (identified by J. W. Gidley). 

 Ptychodus martini AVilliston? 

 Hemiptychodus mortoni Mantell. 



Corax falcatus Agassiz (shark . 

 Lamna texana Roemer (shark). 

 Otodus appendiculatus Agassiz (shark i. 



Ischyrhiza rnira Leidy (identified by J. \V. Gidley). 



The 5 first-named forms have a wide vertical range and are of no value hi close correlation. 

 The species Ptychodus martini Williston? and Hemiptychodus mortoni Mantell are limited in 

 range in tin- ('astern Gulf region to the Mortoniceras subzone; in the western interior region these 

 species occur in the Niobrara formation, but are not known above that formation. These forms 

 may prove of value in correlating the eastern Gulf Cretaceous with that of the western interior, 



i Hyatt, Alphous, Psoudoceratitcs of the Cretaceous: Mon. U. S. Geol. Survey, vol. 44, 1903, p. 206. 



a Stanton, T. W., Succession and distribution of later Mesozoic invertebrate faunas in Xorth America: Jour. Geology, vol. 17, Ko. 5, 1909, p. 419. 



