GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 9 



Several brooks which drain the northern slopes of the Fishkill 

 mountains and the valleys between them join Fishkill creek from 

 the south. Of these, the largest are those leaving the Highlands 

 through Shenandoah hollow and the valley of East Fishkill Hook, 

 and " Clove creek " south of Fishkill Village. Fishkill creek fur- 

 nishes power at Hopewell, Brinckerhoff and Matteawan. 



Casper creek rises near the northern boundary and flows south- 

 west in a rather wide valley to the Hudson which it joins two and 

 one-half miles north of New Hamburg. 



Fallkill creek drains a large area to the north. It flows in a 

 general southwest course to Poughkeepsie where it turns on itself, 

 and, making a large loop, flows north for one-half of a mile and 

 then west to join the Hudson. 



Several brooks, but none of any size, drain the slopes on the west 

 of the Hudson. 



There are no natural lakes or ponds of conspicuous size within 

 the cjuadrangle. Those of any consequence apparently date from 

 the time of the retreat of the ice sheet from this region. 



GENERAL GEOLOGY 



The Fishkill mountains belong to the Highlands province of Pre- 

 cambric rocks. These have their greatest development in Putnam 

 county just to the south. The spurs that have been mentioned 

 are the northern terminations of ridges of gneisses which have a 

 general northeast-southwest trend. Above Peekskill these gneisses 

 are continued across the Hudson into New Jersey. Eastward they 

 extend into Connecticut. 



The summits of the Fishkill mountains, with those of neighbor- 

 ing ones at the south, present a fairly even sky line which may be 

 followed northeastward along the crests of the ridges of the younger 

 rocks. This general uniformity of level is believed by many to 

 mark a former peneplain in this region toward the close of Cretacic 

 time (see plate 3). 



North of the Fishkill mountains are the younger rocks of the area. 

 In general, these do not now tend to climb far up the flanks of the 

 older masses. In most cases the two are faulted against each other 

 and the rocks of the mountains reach close to their bases. In a few 

 places the younger strata extend up a moderate distance on the older 

 rocks and are disturbed relatively little. 



These younger strata rest unconformably upon the Precambric. 

 They are the southwestward representatives of the rocks of western 

 Massachusetts and Vermont and are now known to include strata 



