Maryland Geological Survey 329 



of the Taylor with the upper portion of the ponderosa zone is at once sug- 

 gested, though it cannot be proved until the Taylor is better known. The 

 upper glauconitic clays and sands of the Navarro, however, have yielded 

 a typical Monmouth fauna which includes such diagnostic species as 

 Exogyra costata, Turritella vertebroides, and Sphenodiscus lobaius, 

 together with a large number of less abundant and less ubiquitous forms, 

 a number which will doubtless be greatly increased with the wider knowl- 

 edge of the faunas. 



In Arkansas the presence of Exogyra ponderosa in the Brownstown 

 formation suggests its correlation with the Matawan, while the Marlbrook, 

 Nacatoch and Arkadelphia formations have in common with the Mon- 

 mouth Exogyra costata- and Ostrea subspatulata. 



Correlation With Other American Areas 

 The Upper Cretaceous deposits of Maryland are correlated with other 

 American areas chiefly on the basis of the floras and faunas. A consider- 

 able number of plants identical in species with those of the Earitan and 

 Magothy formations have been found in the western part of the United 

 States, while a number of additional related forms have also been observed. 

 There are very many characteristic genera which are of much value in 

 determining approximate equivalency of the deposits. Compared with 

 the flora of the Dakota sandstone of the Western Interior, the Earitan 

 flora of Maryland furnishes the large number of ten common species, 

 which in itself should refute the opinion of the few geologists who are 

 inclined to consider the Earitan as of late Lower Cretaceous age. 



The Magothy flora is much more closely related to the Dakota flora than 

 is the Earitan flora, and it is believed that the two are in part synchronous. 

 This is indicated not only by the large number of identical and closely 

 related species but by the stratigraphic evidence. The Washita, con- 

 sidered by Hill and others as the uppermost division of the Lower Cre- 

 taceous, contains a fauna and a flora considered by competent paleontolo- 

 gists as Cenomanian in age. It therefore seems probable that the over- 

 lying Dakota is referable to the same stage as the marine Benton, namely, 

 to the Turonian. 



