26 



Introduction 



although he subsequently placed it at a lower horizon. In 1845 de 

 Vemeuil visited North America. He examined the sections in New York 

 in company with James Hall and placed the base of the Devonian at the 

 base of the Oriskany at which point it long remained in most works on 

 American geology. Keyser in his study of the Devonian strata of the 

 Hartz and Bohemia pointed out the Lower Devonian age of the Helder- 

 berg of North America, a conclusion which has been more fully estab- 

 lished by the labors of Clarke and Schuchert. The base of the Devonian 

 is drawn at the base of the Helderberg ' in the present volume, in harmony 

 with the work of the latter investigators. 



The Devonian of Maryland is divided into the following formations 

 and members : 



Upper 



Catskill red sandstone formation 



Jennings sandstone and shale 

 formation 



Chemung sandstone member 

 Parkhead sandstone member 

 Woodmont shale member 

 Genesee black shale member 



•e ! Middle 



Eomney shale formation 



Hamilton shale member 

 Marcelhis black shale member 

 Onondaga shale member 



Oriskany sandstone formation 



Ridgely sandstone member 

 Shriver chert member 



Helderberg limestone forma- 

 tion. 



Becraft member 

 New Scotland member 

 Coeymans member 

 Keyser member 



The Devonian of Maryland forms a part of the Appalachian Province 

 which extends from New York southward in the Appalachian Mountains 

 and Plateau. The resemblance of the formations to those of the north- 

 em part of the area is so close as to establish their essential identity both 

 in lithology and fauna, and hence the similarity of the conditions under 



See the more extended discussion by Schuchert. 



