170 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



view) and the Upper Maysville (McMillan) divisions, the latter in the 

 Appalachian region being an unfossiliferous, gray sandstone apparently 

 of continental origin and equivalent to the Oswego sandstone of the New 

 York section. 



List of Maysville Fossils (Orthorhynchula Bed), Southern Pennsylvania 



Lingula nicTclesi n. sp. 

 Plectorthis plicatella Hall 

 Rafinesquina alternata (Emmons) 

 Raflnesquina squamula (James) 

 Orthorhynchula linneyi (James) 

 Zygospira modesta (Hall) 

 Zygospira ? erratica (Hall) 

 Ischyrodonta unionoides (Meek) 

 Pterinea (Caritodens) demissa (Conrad) 

 Byssonychia radiata (Hall) 

 Byssonychia praecursa Ulrich 

 Allonychia ovata Ulrich 

 Modiolopsis modiolaris (Conrad) 

 Modiolodon truncptus (Hall) 

 Orthodesma nasutum (Conrad) 

 Liospira micula (Hall) 

 Orthoceras lamellosum Hall 

 Isotelus megistos Locke 



THE JUNIATA FORMATION 



Until quite recently American geologists have been in accord in regard- 

 ing the boundary between the Ordovician and Silurian systems as lying 

 at the base of the Bed Medina. Indeed, by many, the base of the Silurian 

 was placed still lower, namely, at the bottom of the Oneida conglomerate 

 which was supposed to underlie the Medina and to be equivalent in age 

 to the Oswego sandstone which actually does occur under the Red Medina. 

 The Oneida conglomerate, however, has been proved to belong at the top 

 of the Medina and may indeed represent the initial deposit of the Clinton. 

 The Oswego sandstone therefore became a valid formation, and the name 

 Oswegan series was coined by Clarke and Schuchert to include the Oswego 



