GLACIAL AND POST-GLACIAL HISTORY 439 



Roye Hook (29, Fig. 9). At its base, both on the north and on the 

 south, there are low-level terraces at about 30 feet. In the Roye 

 Hook hill a large gravel and sand pit shows about 10 feet of fine 

 sand and gravel overlying 5 feet of silt, both sand and silt being hori- 

 zontally stratified, or nearly so. But under the silt there is about 85 

 feet of coarse gravel and sand, with layers dipping at a high angle 

 eastward and southeastward. The gravel and sand in this lower 

 portion of the exposure were not observed to grade into clay, as they 

 were observed to do at Croton, and as they apparently do at Haver- 

 straw. The phenomena at Jones Point and Roye Hook are more 

 nearly allied to deposits which occur in the Highlands than they are to 

 those that occur in the broader part of the valley to the south. These 

 characteristics are discussed in the description of the Highlands phe- 

 nomena. 



THE HIGHLANDS OF THE HUDSON. 



As indicated above in the description of the general features of 

 the Hudson, south of Newburg and Fishkill the Hudson leaves the 

 Appalachian district and crosses through the plateau to the south in 

 that part of its course designated the Highlands of the Hudson. 

 The features of the rock valley here differ radically from those at the 

 north, and in place of a broad dissected lowland between distant 

 uplands, like that in the Appalachian Valley, or of the broad amphi- 

 theater between distant uplands like that at the north edge of the 

 Palisade Ridge at Haverstraw, we have the upland descending 

 abruptly from elevations of 1,100 and 1,400 feet to the waters of the 

 estuary, which is here generally from four-fifths to seven-tenths miles 

 wide, and reaches a maximum width of one and three-fifths miles. 



In this narrow valley the gravel plateaus are present, but if there is 

 a clay plain, it is covered by the waters of the estuary, or is represented 

 by a few limited remnants only. 



The gravel plateaus in the Highlands of the Hudson have charac- 

 teristics which are typical of Class i above described, and indicate 

 the presence of the ice in the valley while these deposits were accumu- 

 lating. There are situations however, where streams of water came 

 from the ice outside of the immediate Hudson River valley and 

 deposited their loads on slopes toward the center of the valley. Such 



