Maryland Geological Survey 43 



in review by Dr. C. A. White in his Correlation Paper on the Cretaceous, 



published in 1891. 



Nearly twenty years after Tyson's discovery of cycad trunks in the 

 iron-ore beds of Maryland, Mr. Arthur B. Bibbins took up the quest, and 

 during the next few years succeeded in obtaining from the inhabitants 

 of the region a very large number of trunks and fragments. These were 

 submitted for critical study to Professor Ward, who in 1894 published 

 a revision of the genus Cycadeoidea, to which all of the Maryland forms 

 belonged. Mr. Bibbins continued to collect more material, and in 1897 

 Professor Ward published descriptions of seven species from Marjdand. 



In a paper entitled " Albirupean Studies," and published in 1892, 

 Professor Uhler makes further contributions to the knowledge of the 

 Potomac, but his stratigraphic conclusions are, according to Professor 

 Ward, set forth in a rather ambiguous manner. 



In a paper in Science, published in 1894, Professor Ward makes an 

 interesting comparison between the Potomac flora and that from the 

 Mesozoie of Portugal made known by the Marquis Saporta. He suggests 

 the following long-range correlations : James Eiver beds = Infra Valan- 

 ginian, Fredericksburg beds = Valanginian, Mount Vernon beds = TJr- 

 gonian, Brooke beds = Aptian, and Earitan beds = Albian. In the same 

 number of Science appeared a note by F. A. Lucas on the Vertebrate re- 

 mains from the Maryland Potomac, Allosaurus, Pleurocoelus, Priconodon 

 and Astrodon being the forms enumerated. The same year Mr. Bibbins 

 published a summary of his Potomac studies, and the Fredericksburg 

 folio of the U. S. Geological Survey by F. H. Darton was issued. It 

 included a large area of the Virginia Potomac, which was described and 

 mapped as a single unit, however. 



A number of important papers appeared during 1896. Among these 

 are Professor Ward's elaborate discussion entitled : " The Potomac For- 

 mation,'" in which he subdivides it into The James Eiver Series, The 

 Eappahannock Series, The Mount Vernon Series, The Aquia Creek 

 Series, The Iron Ore Series, The Albirupean Series, and the Island 

 Series. The flora of each is discussed and considerable space is devoted 

 to the newly discovered flora of the clays on the Mt. Vernon estate. 



