98 NEW YORK STATE MUSEUM 



All ilic icrniccs aii<l i>laiiis in \\w lower IIiulsoii south of Croton 

 jioini, tliosc .11 I'oii \\'asliiTii!:t()n, Collojro Point, Mjuirer, Tarry- 

 lowii and \'an Cortlandt park, accord with this mode of retreat, 

 and the sliu:]ii hut reco^^nizable evidence which they bear of the 

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

 it reasonable to <?rant that the levels which they exhibit are those 

 of local bodies of wat(M' hcdd in position by the i<'e and hence 

 subject to capricious changes. 



Croton point stage. The strongest development of glacial de- 

 ])osits, such as are peculiar to the front of a retreating glacier, 

 in the Hudson valley north of the great terminal moraine in 

 J^rooklyn 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 j)oint the Croton river, a curvilinear stream whose north- 

 ward curvature may be compared with that of the trap ridge 

 which touches the oi)posite shore at Haverstraw. We shall first 

 consider the glacial conditions as they are found at Haverstraw, 

 and tlicn jtrocecd to the interpreta.tion of the deposits at Croton 

 point and in its vicinity, 



Haverstraw (jlacial deposits. The glacial deposits at Haver- 

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

 1o 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 

 op(»ning of (he clay beds atlords numerous op])ortunities for ex- 

 amining their structure and relations. 



Fronldl inonihw. Once the ice front in its retreat lay north 

 of the ciirxcd ridge of trap aboNC referred to, any tendency to 

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

 wai-d ( urving ridge otfei's, and as the ice, on the whole retreating. 



