GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE IO5 



the limestone and the slate and from this point on cascades over 

 the slates until its own delta is reached. It is probably along or 

 very near its preglacial channel from Wolcott avenue southward. 

 The preglacial channel north of here is probably to the southeast 

 of the present course of the stream. 



It may be that during this time of erosion the Hudson cut its 

 present gorge and that the gravel-covered, laminated clays are 

 erosion terraces instead of benches laid down against the ice. 



THE PRESENT DEPRESSION 

 Following the bisection of the Wappinger creek delta, the valley 

 of the Hudson suffered the depression that produced the present 

 estuary and the later channel of Wappinger creek was submerged 

 (see plate 24). Fishkill creek filled up its gorge to tide level and 

 produced its present delta. 



OTHER DRAINAGE FEATURES AND ADJUSTMENTS 



Near Gregory's mill at Old Hopewell, Fishkill creek was deflected 

 by the drift and imposed on the limestone through which it has cut 

 a gorge. 



The rock valley of Casper creek, at points north of the Hope- 

 well branch of the Central New England Railroad, suggests a once 

 more powerful stream which may have drained a larger area to the 

 north of this quadrangle along the valley of the brook that rises in 

 the swamp east of Van Wagner, and now flows north to join a south- 

 ward flowing stream of considerable size, and which reaches Wap- 

 pinger creek by making an abrupt turn to the east-northeast. 



The course of the Fallkill near Poughkeepsie suggests that this 

 stream has utilized certain fault features. Fishkill creek, along its 

 course within the quadrangle, makes a number of bends to the 

 northeast that are in line with the fault features of the Fishkill 

 limestone. 



LAND FORMS 



These are apparently of two fundamental types : those produced 

 by a sort of block faulting and those produced by folding, accom- 

 panied by faulting. Each is distinct, but is modified by the other. 

 Both apparently date from the time of the Green mountain 

 revolution. 



At the close of Cretacic time this region was a peneplain. A re- 

 elevation introduced the history of the present topographic aspect 

 of the quadra^- -rle and subsequent erosion presents the striking dis- 



