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HISTORICAL GEOLOGY. 



Upper, 

 OR Later 

 Devonian. 



Middle 

 Devonian. 



Lower, 

 OR Early 

 Devonian. 



Subdivisions. 



r 2. Chemung Epoch : that of tlie Chemung 

 4. Chemung group, N. Y. Geol. Reports, 1842, 1843. 



Period. 



< 



3. Hamilton 

 Period. 



2. Cornife- 

 rous Period. 



1. Oriskany j 



1. Portage Epoch: that of the Portage group, 

 N. T. Geol. Reports, 1842, 1843. 



2. Hamilton Epoch : that of the Hamilton 

 beds with the Tully limestone in places at top, 

 N. Y. Geol. Rep)orts, 1842, 1843. 



1. Mabcellus Epoch : that of the Marcellus 

 shales (with the Goniatite limestone near the 

 bottom), N. Y. Geol. Reports, 1842, 1843. 



2. CoRNiFEBOus EpocH : that of the Cornif- 

 erous and Onondaga limestones, N. Y. Geol. Re- 

 ports, 1842, 1843. 



1. Schoharie Epoch: that of the Schoharie 

 grit and Cauda-galli grit, N. Y. Geol. Reports, 

 1842, 1843. 



That of the Oriskany sandstone, N. Y. Geol. 



Period : (^ Reports, 1842, 1843. 



The Devonian formations commence in eastern North America with 

 sandstones. Then follows a great continental limestone, the Corniferous. 

 This limestone has in the Devonian era, therefore, a position corresponding 

 with that of the Niagara limestone in the Later Silurian. Above the lime- 

 stone there is a great thickness of shales and sandstones with but little lime- 

 stone. To the eastward, in New York and Pennsylvania especially, the sea 

 border deposits of coarse sands, gravel, and pebble beds, of great thickness, 

 which were in progress during the Upper and partly the Middle Devoiiiah, 

 make now red sandstone and conglomerate, and constitute what is called the 

 Catskill formation. These beds have been heretofore regarded as mainly of 

 subsequent origin to the Chemung, and have been referred to a period follow- 

 ing it, called the Catskill period; but, as explained beyond, they are now 

 believed to be a cotemporaneous formation parallel in its deposition with that 

 of the off-shore and deeper waters of the Chemung period, or Chemung and 

 Hamilton periods, to the westward. 



Over the Eastern Interior region limestones constitute the chief part of 

 the beds of the earlier half of the era, and black shale, of moderate thickness, 

 those of the later beds. 



The three divisions of the Devonian, the Early, Middle, and Later, have 

 been named by H. S. Williams (1894), respectively, the Eodevonian, Meso- 

 devonian, and Neodevonian. The term Brian is applied to the Devonian of 

 North America by Dawson. 



