NEW YORK STATE MUSEUM 



• Devon ic 



Siluric and Lower Devonic formations of the Skunnemunk moun- 

 tain region. The Skunnemunk mountains are a synclinal outlier 

 of Siluric and Devonic rocks extending from the southern Hudson 

 river southwestward into New Jersey. Mr Hartnagel has studied the 

 section through this region made by the Moodna river which emp- 

 ties at Cornwall and describes the rocks as arranged in a spreading 

 fold with some of the members missing from the succession. Thus 

 the order of strata from above downward is as follows: 



Monroe shale 



Oriskany sandstone 



Port Ewen limestone 



and ■ «, 



I Becraft limestone 



I Not exposed 



New Scotland limestone 



Coeymans limestone 



(Erosion intreval) 



Manlius limestone 



Rondout waterlime 



Cobleskill & Decker Ferry limestone 



c T3- 4. j , t Upper Siluric 



T , i , \ Bmnewater sandstone - 



LongWO ° dshale= | High Falls shale 



Shawangunk conglomerate . J 



(Unconformity) 



Hudson River shale Lower Siluric 



In contrast to the abrupt change in sedimentation at the close 

 of the period of the Shawangunk grit in Ulster county, in this sec- 

 tion the Longwood shale follows the Shawangunk without break. 

 It has been quite generally considered that the Shawangunk grit is 

 of equivalent age to the Oneida conglomerate of central New York 

 and, in textbooks and general writings, both have been accepted 

 as representing the base of the Upper Siluric. This was a natural 

 inference so long as the Cobleskill formation was looked, upon as 

 of Niagaran age but as the latter is now known to be ofTlater age 

 than the Salina deposits and as the Longwood shales and Shawan- 

 gunk grit in this section follow each other without break, F one must 

 conclude that these two formations are of much later! geologic 

 date than formerly supposed and it is probable that the Shawan- 

 gunk grit represents the invading basal member of the Salina for- 

 mation in the eastern part of the State. 



