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tTNITED STATES NATIONAL MUSEUM BULLETIN 215 



Coastal Plain." Recent studies (Murray, 1955) have 

 shown that the "basal Wilcox" of some areas is a 

 "late Midway" time equivalent. The recognizable 

 sedimentary facies of the Midway and WUcox groups 

 are thus not entirely time equivalents. The Wilcox 

 is considered to be lower Eocene, yet strata in other 

 areas have been referred to the Wilcox, on lithologic 

 bases, which are fatmally much closer to the Midway 

 (Paleocene) . 



As was demonstrated by Murray (1955), confusion 

 has arisen by the varying usage of the terms Midway 

 and Wilcox by some authors in a lithologic sense (rock 

 unit) and by others in a time connotation (time-rock 

 unit). The greater use of the European stage names or 

 of faunal zones in determining correlations would avoid 

 these misinterpretations. 

 Salt Mountain Limestone 



The Salt Mountain limestone of Alabama is recog- 

 nized by the U. S. Geological Survey to be of lower 

 Eocene age and to belong to the Wilcox group (Wil- 

 marth, 1938, p. 1898). It is regarded as lying between 

 the Tuscahoma sand and the Nanafalia formation, 

 although it does not appear in contact with these 

 formations, the only known outcrops being at Salt 

 Mountain and in its immediate vicinity. Toulmin 

 (1941, p. 569) recorded 99 species of Foraminifera from 

 the Salt Mountain, of which 19 were common to the 

 upper Wilcox greensand at Ozark, Alabama, 10 oc- 

 curred also in the upper Wilcox (Bashi) of Woods Bluff, 

 Alabama, 11 occurred in the lower Midway (Kincaid) 

 of Texas, 18 in the upper Midway of Texas, and 14 

 were found in common with a Midway fauna in Ala- 

 bama. Thus the Salt Mountain limestone has about 

 the same number of species in common with the 

 Midway elsewhere as it does with the Wilcox, although 

 Toulmin considered that at least the upper part was 

 younger than Midway and probably of early Wilcox age. 



Aquia Formation 



The Aquia formation of Maryland has been con- 

 sidered by the U. S. Geological Survey to be lower 

 Eocene in age. Cooke and Stephenson (1928) con- 

 sidered the Vincentown formation of New Jersey to be 

 the equivalent of the Aquia formation of Maryland, 

 considering both to be of Wilcox Eocene age. MiUer 

 (1956) concurred in this determination, on the basis of 

 megafossils. ShiiHet (1948) described the Foraminifera 

 of the Aquia, and stated (p. 17) that the Aquia was 

 "considered equivalent to the lower Wilcox of the Gulf 

 Coast and to the Ypresian of Europe." She recorded 

 nine species of planktonic Foraminifera. 

 Brightseat Formation 



The Brightseat formation of Maryland was recently 

 described as of Paleocene age, and underlies the Aquia 

 formation. 

 Vincentown and Hornerstown Formations 



Both the Vincentown and Hornerstown formations of 

 New Jersey were originally described as of late Creta- 

 ceous age (Clark, Bagg, and Shattuck, 1897, p. 326), 



but younger than the Upper Cretaceous of the Gulf 

 Coastal region, and the equivalent of the European 

 Danian stage. Cooke and Stephenson (1928, p. 141) 

 placed these strata in the Eocene (in 1928 the U. S. 

 Geological Survey did not recognize the Paleocene as a 

 distinct epoch), on the basis of macrofossU evidence, as 

 well as diastrophic evidence that the Hornerstown marl 

 transgressed southward on successively older Creta- 

 ceous beds. They also correlated the Vincentown 

 formation with the Aquia formation of Maryland. 

 Canu and Bassler (1933, p. 3) correlated the Vincen- 

 town with the Maestrichtian and Danian (Upper 

 Cretaceous) of Europe, on the basis of the Bryozoa, but 

 also noted a similarity of the fauna to that of the 

 Aquia of Maryland and the Clayton formation (lower 

 Midway) of the Gulf Coast. Brotzen (1948, p. 32) 

 correlated the Vincentown with the Thanetian, Lande- 

 nian (Paleocene) and the Ypresian (lower Eocene). 

 McLean (1953, p. 1) identified Paleocene benthonic 

 Foraminifera in the Vincentown, as well as some species 

 suggestive of the Wilcox Eocene, and believed the 

 Vincentown to represent transitional strata. 



Fox and Olsson (1955, p. 736) placed the Horners- 

 town formation in the Paleocene and the Vincentown 

 was said to contain a "mixture of typical Paleocene 

 forms in association with new Eocene elements charac- 

 teristic of the upper part of the Vincentown." They 

 considered the Vincentown to be "clearly Eocene in 

 age." Hofker (1955, p. 1) listed 22 species of Foramin- 

 ifera common to the Vincentown and the Paleocene of 

 Em-ope, and considered the Vincentown to be lower 

 Paleocene. 



Miller (1956, p. 731) studied the invertebrate fauna 

 of the Vincentown and concluded that the "strongest 

 aflfinities are to the Lower Eocene (Aquia) of Maryland 

 and the Danian of Denmark." He recorded 18 species 

 common to the Vincentown and Aquia, including 

 bryozoans, ostracods, alcyonarids, and moUusca. How- 

 ever, as the Aquia was considered lower Eocene, he 

 also correlated the Vincentown with the lower Eocene. 

 He stated (p. 732) that the "NautUus" danicus, bryo- 

 zoans and alcyonarids were also found in the Danian 

 of Eiurope, but he considered them "facies fossils." 



Correlation by Planktonic Foraminifera 



There is no longer any reason for questionable cor- 

 relations of marine deposits at the Cretaceous-Tertiary 

 boundary. Wherever planktonic Foraminifera occur 

 they show a very pronounced faunal break. The 

 planktonic genera characteristic of the Cretaceous 

 {Globotruncana, Rugoglobigerina, Hastigerinoides, etc.) 

 are never found in the Cenozoic, and do not occur in 

 the type Danian or in any Paleocene strata. Typical 

 Cenozoic Glohorotalia and Globigerina, such as are 

 found in the Paleocene (Danian, Midway, etc.) the 

 world over, do not appear anywhere in the Cretaceous. 

 Thus a Cretaceous age is definitely excluded for strata 

 in which they appear. 



As has been shown by Bolli, Loeblich, and Tappan 



