PREFACE 



The present volume is the fourth of a series of reports dealing with 

 the systematic geology and paleontology of Maryland, the Eocene, Mio- 

 cene, and Plio-Pleistocene deposits having already been fully described. 



The Lower Cretaceous deposits which form the subject-matter of the 

 present volume are more fully developed in the Maryland- Virginia area 

 than anywhere else in eastern North America and the Maryland section 

 is the type for the whole Atlantic coastal plain. Similarly the faunas 

 and floras of the Lower Cretaceous are much more fully represented than 

 elsewhere in this general region, the flora in particular being the richest 

 known flora of this age. 



The vertebrate fauna of the Arundel form.ation collected by Mr. John 

 B. Hatcher and studied by the late Professor 0. C. Marsh of Yale Uni- 

 versity is of interest, since it is the only Lower Cretaceous vertebrate 

 fauna known east of the Mississippi Eiver, and it was upon these materials 

 that Professor Marsh based his opinion that the Potomac was of late 

 Jurassic age. This fauna has been thoroughly revised and elaborated in 

 the light of additional collections by Professor E. S. Lull of the same 

 institution. His results are in agreement with the evidence of the fossil 

 plants, that these deposits are of Lower Cretaceous age. 



The invertebrate faunas, while meagre and poorly preserved, are of 

 great interest, since they constitute the only known representation in 

 eastern North America of the estuarine and fluviatile invertebrate life 

 of the Lower Cretaceous. This fauna has been described by Professor 

 W. B. Clark of the Johns Hopkins University. 



The fossil floras have been restudied by Mr. E. W. Berry of the Johns 

 Hopkins University. The difficulties in the way of an adequate study 

 of the Potomac flora are very great. The material, with the exception 

 of silicified wood, lignite, and the silicified trunks of Cycadeoidea, is all 



