UPPER SILURIC AND LOWER DEVONIC FORMATIONS 

 OF THE SKUNNEMUNK MOUNTAIN REGION 



BY . 



C. A. HARTNAGEL 



Introduction 



The Upper Siluric and Lower Devonic formations of the 

 Skunnemunk mountain region, in the vicinity of Cornwall, 1 

 Orange co., N. Y., are the extreme northeastern portion of a 

 great outlier of rocks which extends from near Cornwall station 

 southwestward into New Jersey for a total distance of about 50 

 miles. 



The general structure of the rocks of this area is that of a 

 great syncline which is, however, much modified by secondary 

 folds and by faulting. The trend of this syncline is parallel to, 

 and 23 miles southeast from, the main area of the formations of 

 similar ages, which outcrop approximately along a line extending 

 from Rondout, N. Y., southwesterly through Port Jervis and 

 continuing into New Jersey. 



Near the northern extension of Skunnemunk mountain, the 

 Moodna river flows in a direction a little north of east. On 

 reaching the end of the mountain, the river abruptly turns and 

 flows southeasterly, in what is apparently a fault valley and 

 across the strike of the Upper Siluric and Devonic formations. 

 The river then again turns and flows towards the northeast and 

 finally empties into the Hudson river at Cornwall-on-the-Hudson. 



Within the V-shaped area made by the somewhat unusual 

 course of the Moodna river, there is a comparatively small syn- 

 cline, and it mainly is to this section that this paper will be 

 restricted. 



Previous work on this area. The rocks of this section have 

 been differentiated since the early days of the New York State 

 Geological Survey. Forming as they do an outlying area, they 

 have naturally offered to the geologist an opportunity for care- 

 ful comparative stratigraphic and paleontologic work. Hor- 

 ton was the first to give an account of this district [An. Rep't. 



1 Id]ewild is the name of the postoffice at Cornwall station on the Newburgh branch of the 

 Erie Railroad. This station is but a few hundred yards from the cut on the Ontario and Western 

 Railroad. The nearest station of the latter road is at Orr's Mills less than J mile away. 



