GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE IO3 



Well-preserved sand and gravel erosion terraces occur at fre- 

 quent intervals along Wappinger creek. These are best shown in 

 the open portion of the valley of this stream in the neighborhood 

 of Manchester Bridge and between that hamlet and Rochdale. The 

 road from Manchester Bridge to Rochdale for a mile north of the 

 former place closely follows the edge of a fine terrace that drops 

 with uniform slope from the i6o foot level to the present flood 

 plain of the creek. The cemetery at Manchester Bridge is built 

 on a projecting tongue of this fine terrace which is broken by the 

 limestone knoll on which Mr George Byer's house stands. North 

 of here it may be followed for a short distance. 



South of Rochdale, to the east of the Pleasant Valley road, on 

 the west side of the creek, the present flood plain makes a large 

 embayment to the west, north of Frank De Garmo's house. This 

 embayment is fringed by a fine terrace, a portion of which is shown 

 in plate 20. Other terrace remnants may be followed southward 

 along the creek. 



These dissected deposits clearly belong to an epoch when the 

 creek valley was flooded and the creek was able to aggrade its 

 valley floor to the level of these terraces, at least. It was probably 

 during this time that the delta deposits were making at the mouth 

 of the creek, whatever the conditions there may have been. These 

 features would appear to have been intimately connected with the 

 retreat of the ice sheet which, as it melted, would have furnished 

 both the floods and the material. This material is in the form of 

 sand and gravel. A good deal of finer detritus must have been 

 carried out into the Hudson gorge. 



To allow for this accumulation of sand and gravel in the old 

 valley of the creek, either there must have been a body of standing 

 water in the Hudson gorge nearly 200 feet higher than now, or the 

 land must have been much lower than now. 



Fishkill creek and its tributaries were also able to aggrade their 

 valley floors. Gravel deposits belonging to a former higher level 

 form imperfect terraces at different points. In some places, the 

 gravels look like outwash plains during a short halting of the ice, 

 as in the vicinity of Hopewell Junction. The Newburgh, Dutchess 

 & Connecticut Railroad apparently cuts a series of terrace remnants 

 from Hopewell to Brinckerhoff. Fishkill Village is located on a 

 terrace at the 200 foot level which extends southwest to Glenham. 

 Small, but perfect, terrace levels along brooks tributary to Fishkill 

 creek, belonging to a stage in the subsidence of the water correspond- 



