GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 95 



minute size to the dimensions shown in plate 19. These features are 

 more common at the east. 



Cleavage is so prominent in surface outcrops that the stratifica- 

 tion dip is usually obscured. The prevailing eastward dip indicates 

 a common eastward inclination for the cleavage. The presumption 

 is that stratification and cleavage often coincide or approximate each 

 other very closely. Where the cleavage is not dominant to the 

 exclusion of the stratification, this fact is often observed. 



Jointing is well displayed in Matteawan along the Newburgh, 

 Dutchess and Connecticut track. A prominent set of joints shown 

 here has a general strike of n. 20° e. and a dip of 80° w. 



Some of the faults within the slates have been alluded to in 

 describing the limestone patches within this formation. 



Extending in a northwest direction approximately parallel with: 

 the road from Brush to Arthursburg, as shown on the map, is a 

 clear transverse fault. This break is best seen from the southeast 

 near the old railroad bed. This break intersects a line of strike 

 faulting at Arthursburg, and probably ends at that point. The 

 strike fault just mentioned dies away to the northward. Continued 

 south, it bounds the limestone triangle north of Hopewell Junction 

 on the west. 



The high hill northwest of Lagrangeville is bounded by a fault 

 scarp on the west. This scarp is a conspicuous cliff east of the 

 road from Lagrangeville to Freedom Plains. The high hill north- 

 west of Billings is bounded on the south by an east-west fault 

 whose scarp is very conspicuous. 



The other lines of fracture shown on the map have already been 

 referred to. 



A long line of swampy lowland, beginning two miles north of 

 Freedom Plains and running northward toward Pleasant Vallev, 

 appears to mark a line of crustal weakness similar to that which 

 extends from Hopewell Junction to Manchester Bridge. 



The fault which bounds the western strip of the Wap])inger creek 

 limestone on the north may extend across the Hudson and bound 

 '' Illinois mountain " on the north. 



Metamorphism and alteration. The members of the slate 

 formation show an appreciable increase in metamorphism toward 

 the east within the quadrangle, passing into slaty phyllites and gray- 

 wackes. These rocks do not develop into perfect schists like those 

 occurring a few miles to the eastward, but pellets of decomposed 

 ferruginous particles, suggesting former garnets, were noted in the 

 phyllites east of Arthursburg. Veins, veinlets and nests of quartz 



