74 NEW YORK STATE MUSEUM 



ELEVATIONS OF THE HUDSON ROCK TERRACES 



Kings Bridge 200 



Yonkers 350 



Tarrytown 140 



Sing Sing . 160 



Croton 140 



Peekskill. Verplanck and Buchanan 140 



Garrison 200 



Cold Spring 220 



Dutchess Junction 160 



Poughkeepsie 200 



Albany 220 



Schuylerville 300 



Mouth of the Moses kill 200 



The rock terraces bordering the Hudson gorge are rather uni- 

 form in elevation. The terraces are higher now on hard than 

 on soft rocks, higher in the Archaean belt of the Highlands and 

 southward to Yonkers and over the Palisades than elsewhere; 

 lower on the soft Hudson shales and slates and in the region of 

 the Triassic sandstones. The lowness of the terrace on the east 

 bank between Peekskill and Dobbs Ferry is accounted for by the 

 former overlap of the Triassic basal beds in this region ; but these 

 differences of level are not all accounted for by differential erosion, 

 including glaciation and weathering, as between the hight in the 

 Highlands and about Yonkers. The terrace hight from Sing Sing 

 southward to Kings Bridge appears too high, and in view of the 

 rapid falling off of the terrace level in New York city and as 

 marked by the decline of the Palisade ridge in Hoboken and 

 southward to its pre-Cretaceous level, indicates a local uplift, 

 central about Y r onkers. 



The narrowness and local absence of the rock terrace within 

 the Highlands is to be taken as evidence of the slower or belated 

 cutting through the Archaean rocks of that district. The terrace 

 is clearly shown, however, at West Point, Highlands Station 

 and Garrisons, and appears to have extended through the High- 

 lands as the old floor of the Hudson valley, thus indicating the 

 existence of a water gap here at a time as remote as the epoch of 



