GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 57 



THE CENTRAL STRIP 



Boundaries. This strip enters the quadrangle from the north 

 at Pleasant Valley. Its eastern margin forms the western bank of 

 Wappinger creek north of the covered bridge at Pleasant Valley 

 and southward follows the creek closely as far as Rochdale. At 

 this place the limestone is in contact with the slate at the dam and 

 on the island just below it. South of Rochdale the limestone fol- 

 lows the creek for one-half mile and then bears slightly to the west. 

 It apparently ends just north of the terrace one- fourth of a mile 

 east of Tompkins's house (see plate 17) on the Pleasant Valley road. 

 This terrace fringes an old meander of the creek and extends around 

 to the south side where the limestone appears again just south of 

 the road that skirts its edge. East of the portion of this road run- 

 ning north and south, just west of Frank De Garmo's house, are 

 numerous outcrops of the slates, but these disappear at the terrace 

 slope and no outcrops appear in the deep westward embayment 

 formed by the old meander. 



This embayment is regarded as lying in a zone of transverse 

 faulting. It seems probable that the slates were dropped down in 

 here. At any rate, either on this account or because of faulting, a 

 weakness was produced which the base-leveling forces caught and 

 finally left as a gap in the ridge of limestone. It seems probable 

 from the dimensions of certain faulted limestone blocks a short dis- 

 tance to the eastward that they belong in or near this gap. The 

 slate has been dropped between the faulted masses and the dis- 

 membered main strip. 



South of the break in the central strip its eastern margin follows 

 the road until the latter turns eastward and then extends as a con- 

 spicuous wooded scarp in a north and south line to a point about 

 one-third of a mile south of Frank De Garmo's house. At this 

 point the limestone sends a sharp angular spur eastward for about 

 200 yards, as shown on the map. The strike of the slates just west 

 of De Garmo's house, projected southward, would bring them sharply 

 against the limestone in the included angle of this spur, showing a 

 transverse fault between the slates and the spur and indicating that 

 the eastern marginal scarp south of De Garmo's is a faulted one. 



Limestone outcrops at the apex of this spur, whence it may be 

 traced by continuous outcrop along the margin of the slate to and 

 across the railroad track and highway west of Manchester Bridge. 

 South of here the eastern margin follows the eastern base of an 

 immense drumlin and south of this distinctly to the Poughkeepsie- 



