FORMATIONS OF THE SKUNNEMUNK MOUNTAIN REGION 41 



midway between the outer faces of the syncline, the Oriskany 

 and Cornwall (=Monroe) formations rise as a high elevation 

 "known as Pea hill. This hill extends about a mile to the south 

 where, at its base, the Moodna river flows and which, as already 

 indicated, cuts off this area from Skunnemunk mountain. 



At first sight it would appear that this trough is a pitching 

 syncline, and its present condition produced as a result of greater 

 ■erosion of the northeast end which here would bring the two 

 limbs close together. This, however, can be regarded as only 

 one of the factors which indicate a spreading fold. The nearly 

 vertical strata in the railroad cut are conditions which could not 

 have been brought about by any method of erosion alone, but it 

 must be concluded that the narrowness of the fold at one end is 

 indicative of an originally spreading fold and, therefore, that 

 its present appearance is not due simply to erosion. 



As the axis of this fold passes considerably to the east of the 

 axis of Skunnemunk mountain, it is regarded rather as a local 

 development and not an extension to the northeast of the main 

 syncline which forms Skunnemunk mountain. 



Geological formations. The rocks involved in this area from 

 the top downward are as follows: 



Cornwall (=Monroe shales of Hamilton age) 



Oriskany sandstone 



Port Ewen ( ?) limestone 



Becraft (?) limestone 



New Scotland limestone 



Coeymans limestone 



Manlius limestone 



Rondout waterlime 



Cobleskill and Decker Ferry limestones 



Binnewater quartzite | =Longwood shales (Ontaric) 



High Falls shale } of Darton 



Shawangunk conglomerate J 



"" Hudson River " shales. . Lower Siluric (Champlainic) 



Cornwall shale. For reasons stated below, this term is used 

 in place of the name Monroe shales which was introduced by 

 Darton 1 to designate the shales carrying a sparse Hamilton 

 fauna, which are w T ell developed in the towns of Monroe and 

 ■Cornwall in Orange county. In view of the fact that the name 

 "" Monroe beds " had been used by Dr A. C. Lane to include all 

 the' rocks between the .Niagara and Dundee limestones of Michi- 

 gan, and also since there was some doubt as to the validity of 

 the Michigan name, Professor Prosser submitted the matter to 



1 Geol. Soc. Am. Bui. 1894. 5:374. 



>-Devonic 



Lpper Siluric 



