CHAPTER XIX 

 THE DEVONIAN PERIOD 



FORMATIONS AND PHYSICAL HISTORY 



Early in bhe Devonian period, the sea covered the present area 

 of land to some such extent as shown in Fig. 407. During the 

 period, there were changes in the relations of land and water, some 

 of which were of great importance in their effects on the life of the 

 period. 



The Devonian system, like its predecessors, is conveniently 

 divided into a Lower, a Middle, and an Upper portion. The sub- 

 divisions now recognized in New York (the state where the Devo- 

 nian is best developed and known) are as follows : 



( Chautauquan Chemung and Catskill 

 Upper Devonian 4 ( Portage beds 



(Senecan \ Genesee shale 



Devonian < 



( Tully limestone 

 c^ . ( Hamilton shale 



{ Marcellus shale 

 Middle Devonian < f Onondaga (Corniferous 



vonian < 





Esppus grit 

 Orisk 



(Oriskanian Oriskany beds 



( Kingston beds 

 HeMerbergian i ^^SS 

 [_ Coeymans limestone 



The subdivisions in the last two columns are not applicable in 

 detail to regions remote from New York. Of the above formation 

 names, Helderberg (or Helderbergian), Oriskany, Onondaga (Cor- 

 niferous), Hamilton, Portage, and Chemung, have widest application 



1 As originally classified, there was a Lower and an Upper Helderberg 

 formation. The latter is now more commonly known as the Onondagan (Cor- 

 niferous) . In this volume the term Helderberg is applied to the former only. 

 The adjective " lower " therefore becomes superfluous. 



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