214 CLARK AND BIBBINS — GEOLOGY OF THE POTOMAC GROUP 



Arundel and Patuxent formations. Further investigations of these floras 

 may, to be sure, lead to other conclusions, but large collections have 

 already been made, and the paleobotanists who have studied them have 

 registered their decision regarding the Cretaceous age of the deposits in 

 no uncertain way. 



From our present knowledge of the floras and faunas it is apparent 

 that there is considerable disparity between the evidence afforded by 

 vertebrate paleontology and by paleobotany. At least such is the case 

 if equal consideration is given the conclusions of each group of investi- 

 gators. It seems essential, however, to suspend final decision of these 

 questions until more exhaustive investigation of the faunas and floras 

 has been made throughout the entire Coastal region. The authors there- 

 fore temporarily place the boundary line between the Jurassic and Cre- 

 taceous at the base of the Patapsco formation, but with the feeling that 

 much doubt exists regarding it, and that the question is far from settled. 



Study of scientific and economic Collections 



A large number of new stations yielding fossil plants have been found 

 by the authors, and the collections of silicified stems of Cycadeoidea 

 (plate 28, figure 1) from the middle and lower Potomac have reached 

 more than a hundred specimens. The collection of silicified and limon- 

 itized coniferous woods and lignites has likewise been much increased. 

 A large dicotyledonous flora has also been collected from the upper for- 

 mations. These materials are undergoing monographic study by Ward, 

 Knowlton, and Fontaine. 



One notable addition has been made to the collection of Arundel 

 clinosauria — a rib of an exceptionally large dinosaur in a condition of 

 preservation quite unusual in the Arundel beds. This bone, together 

 with the large femur excavated in 1895 and a number of other fragments 

 of huge bones and large teeth (plate 28, figure 2) found at widely sepa- 

 rated stations, clearly show what has not been generally supposed, that 

 gigantic as well a&diminutive-dinosauria inhabited the Arundel swamps. 

 One of these, according to Lucas, who has undertaken the extremely 

 difficult task of deciphering these mostly fragmentary remains, reached 

 at least 40 feet in length. 



Two localities in the Arundel of Maryland have yielded molluscan re- 

 mains. These have been placed in the hands of Stanton for study. 



Extensive collections illustrating the highly varied economic deposits 

 of the Potomac terrane have also been made, notably of clays, whose 

 study by Ries has already reached completion. The results of these 

 several studies, as well as those of the authors, will later appear in 

 monographs of the Maryland Geological Survey. 



