404 



Report of the State Geologist. 



Monroe shales. These are dark grey or black slaty shales and slates, 

 which are usually fossiliferous. They extend around the base of Skunne- 

 munk mountain, and along the eastern base of Bellvale mountain. 



Their thickness in the former ridge is probably not over 200 feet, but 

 their greatest development is in Pea hill, near Cornwall. 



Bellvale flags. These overlie the Monroe shales, and are represented 

 by a series of thin-bedded sandstones with occasional shaly partings and con- 

 cretionary layers. They pass into the underlying Monroe shales, and upward 

 into the conglomerate. Normally, the Bellvale flags are moderately fine- 

 grained sandstones of grey color. In their upper layers, near the transition 

 into the conglomerate, they become massive, quartzose and coarse. The 

 sandstones are also traversed by numerous thin veins of milky quartz. The 

 flags extend from the New Jersey state line to the north end of Skunnemunk 

 mountain, where they terminate somewhat abruptly. The thickness of the 

 Bellvale flags is about 1,000 feet. 



Ska >i in in a id- conglomerate. In its typical development this rock is 

 composed of an aggregate of quartz and some shale pebbles in a matrix of 

 reddish quartz and argillaceous material. The pebbles are generally one to 

 two inches in diameter, but sometimes attain a size of several inches. Local 

 layers of red slate occur interbedded with the conglomerate in the upper 

 portions and are well seen in the road over the mountain from Greenwood 

 lake to Warwick. The conglomerate passes downward through a pebbly 

 quartzite and red quartzitic sandstone into the Bellvale flags. It can not be 

 said that these intermediate beds of passage belong to one member more than 

 the other. The conglomerate caps Bellvale and kSkunneniunk mountains and 

 gives rise to high cliffs and steep ledges. Professor Smock has estimated, and 

 probably correctly, the thickness of the Skunnemunk conglomerate as 300 

 feet, but in Bellvale mountain, to the south, it is much thicker, not far from 800 

 feet. Mr. Darton considers that the Skunnemunk conglomerate may possibly 

 represent the Oneonta formation, as the deposition of the latter in central 

 New York was characterized by an abrupt change in the nature of the sedi- 

 mentation, or it may represent the coarse Chemung beds of the southern 

 Catskills or, thirdly, may be a purely local feature. 



Chemung Group. This formation is only present in the western portion 

 of Deer Park tow nship. The beds are mostly unfossiliferous sandstones, w ith 

 some interbedded shales. The divisions occurring within the limits of the 

 comity are the Delaware flags, New Milford red shales, Starucca sandstone 

 and Chemung sandstones, of Prosser. 



