454 



HISTORICAL GEOLOGY 



Fig. 426. — Map showing the probable outline of 

 North America during a portion of the Middle Devonian. 

 Solid black shows continental deposits. (Modified after 

 Schuchert.) 



The Devonian in New 

 York. — There are three 

 Devonian formations in 

 New York which deserve 

 especial mention: the 

 Oriskany, the Onondaga, 

 and the Catskill. The 

 Oriskany is a sandstone 

 formation made, for the 

 most part, of clean beach 

 sands, which in New York 

 is from a foot to several 

 feet thick and in the 

 Middle Atlantic States is 

 several hundred feet thick. 

 The formation indicates a 

 raising of the land or an 

 increase in the rainfall, or 

 a combination of the two, 

 since stronger currents are 

 necessary to supply coarse 

 waste. 



The Onondaga lime- 

 stone with its wealth of 

 corals and brachiopods in- 

 dicates warm, clear seas 

 of long duration sur- 

 rounded by low lands. 



The Catskill formation, 

 thousands of feet thick, 

 extends from Virginia to 

 the Catskill Mountains in 



New York and is a great delta deposit, made of alternate layers of sandstone and 

 shale, sometimes the one and sometimes the other predominating. Upon this assump- 

 tion the whole constitutes a delta. The form of the plain was probably somewhat 



<Sea level 



Ordovician 



Fig. 427. — A Section in New York state showing the relation of the Ordovician, 

 Silurian, and Devonian. (After W. J. Miller.) 



similar to that of the high plains region of the western interior of North America 

 (p. 588) (Harrell). 1 While the Catskill delta was being built up, muds were accu- 

 mulating in the shallow seas (Portage and Chemung). 



1 Barrell, J., — The Upper Devonian Delta of the Appalachian Geosyncline: Am. Jour. Sci., 

 Vol. 36, 1913, pp. 429-472 ; and Vol. 37, 1914, pp. 87-109, 225-253. 



