96 NEW YORK STATE MUSEUM 



are most abundant in the northeastern part of the area. Sandstones 

 have been changed into quartzites. 



Summary. There is no evidence at hand that any slates of 

 the quadrangle are older than the limestone conglomerate that has 

 been discussed, either as overlying the Beekmantown or as isolated 

 inliers within the slates. The slate formation was ushered in by 

 this basal conglomeratic layer. The area of deposition of the latter 

 may have been much more extensive than is indicated by its present 

 faulted outcrops. The period of its formation was of short dura- 

 tion. 



The most that can be said of the slate series is that it began in 

 some horizon of the Trenton and perhaps ranges upward an 

 indefinite distance into the Cincinnatian. Probably a large portion 

 is of Trenton age. 



The Utica may be present, although the graptolite beds that have 

 been so called more probably represent an early invasion of the 

 Utica fauna in Trenton time in what is known as the Normanskill 

 subepoch. Some of the slates may be contemporaneous with the 

 Utica as developed elsewhere to the north, and possibly even 

 younger; or they may all be of Trenton age. 



PREGLACIAL HISTORY OF THE DRAINAGE 

 Old valleys of the Tertiary cycle. During the erosion cycle 

 inaugurated by the Postcretacic uplift, the Hudson river then, as 

 now, must have been the dominant factor in the drainage of this 

 and adjacent areas. A broad valley region was formed and the 

 tributaries of the master river steadily pushed their valleys 

 eastward. The early Tertiary valley of the Hudson itself is now 

 represented by old rock terraces preserved at different points back 

 from the river's edge. Near Poughkeepsie they have an elevation 

 of about 200 feet. 



The rock valleys of the present tributary streams are in most 

 cases out of proportion to the present size of those streams. Dur- 

 ing the time the Hudson river occupied the valley now marked by 

 the terraces that have just been alluded to, its tributaries widened 

 their own valleys a good deal and acquired their present open char- 

 acter. These branches formed a drainage system of the second 

 order within the broad valley region of the main river and a some- 

 what advanced stage of mature topography was attained. During 

 this time the various lines of crustal weakness became marked off 

 into their present prominence, without necessarily becoming prom- 

 inent lines of drainage; simply responding in a logical way, on 



