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NEW YORK STATE MUSEUM 



All the terraces and plains in the lower Hudson south of Croton 

 point, those at Port Washington, College Point, Maurer, Tarry- 

 town and Van Cortlandt park, accord with this mode of retreat, 

 and the slight but recognizable evidence which they bear of the 

 presence of the ice along this eastern bank of the Hudson makes 

 it reasonable to grant that the levels which they exhibit are those 

 of local bodies of water held in position by the ice and hence 

 subject to capricious changes. 



! Croton point stage. The strongest development of glacial de- 

 posits, such as are peculiar to the front of a retreating glacier, 

 in the Hudson valley north of the great terminal moraine in 

 -Brooklyn and south of the Highlands, occurs at a point in the 

 valley where there is again an important change in the geologic 

 structure of the region. At Haverstraw, the thick sill of in- 

 trusive basalt which forms the palisades of the western bank of 

 the river curves inland and westward, presenting its steep front 

 to the north. At the same time the Hudson valley eroded in the 

 Triassic basal beds widens out to the westward, and the gorge 

 occupied by the existing river from Ossining (Sing Sing) north- 

 ward bends around in deference to the geologic structure of its 

 western bank. On the east bank there debouches just south of 

 Croton point the Croton river, a curvilinear stream whose north- 

 ward curvature may be compared with that of the trap ridge 

 which touches the opposite shore at Haverstraw. We shall first 

 consider the glacial conditions as they are found at Haverstraw, 

 and then proceed to the interpretation of the deposits at Croton 

 point and in its vicinity. 



Haverstraw glacial deposits. The glacial deposits at Haver- 

 straw from the base of High Tor northward along the shore and 

 to Stony Point, for a mile or more inland, are rather complex, 

 consisting of the more striking brick clays, glacial sands, gravels, 

 and also till in the form of a frontal moraine. The extensive 

 opening of the clay beds affords numerous opportunities for ex- 

 amining their structure and relations. 



Frontal moraine. Once the ice front in its retreat lay north 

 of the curved ridge of trap above referred to, any tendency to 

 move southward would be met by the obstruction which this west- 

 ward curving ridge offers, and as the ice, on the whole retreating, 



