360 New York State Museum 



Western Devonian can seldom be correlated with those 

 in the East, as such a different succession of physical 

 events are indicated. 



The Devonian period had a little more than half the 

 duration of Ordovician time and closed with almost 

 complete emergence of the continent. As we have 

 seen, besides in New York State, Devonian rocks out- 

 crop in the Michigan area and extend into Wiscon- 

 sin and Iowa, Ohio, Indiana and Ontario, Canada. 

 Occurrences are also found in Oklahoma, Missouri and 

 western Tennessee and Kentucky. Along the line of 

 the Appalachians Devonian rocks have been traced, 

 with interruptions, from southwestern Virginia to 

 Albany, N. Y. In the St Lawrence region deep de- 

 posits occur in the Gaspe area. Northern Nova Scotia 

 and northern Maine also have these rocks. In the 

 west Devonian strata, often in considerable thickness, 

 occur in the Rocky mountains and in the Canadian 

 northwest; Devonian beds occur even far north on the 

 shore of Kennedy channel, 80° N. latitude. Devonian 

 rocks in New York state have a total thickness between 

 8000 and 9000 feet, the Catskill mountains along the 

 Hudson representing the most impressive single ac- 

 cumulation of Devonian deposits in the United States. 

 In the northern Appalachians the deposits are mostly 

 shales and fine-grained sandstones and here are found 

 the thickest series of Devonian beds in the country 

 representing the longest sequence. Pennsylvanian de- 

 posits show the greatest thickness, 13,000 feet of 

 shales and sandstones which become less marine, 

 coarser and redder toward the top. Here the Lower 

 Devonian has a thickness of about 250 to 400-f- feet, 

 the Middle Devonian of about 1400 to 2750 feet, the 



