GLACIAL AND POST-GLACIAL HISTORY 435 



(2) The ice retreated so that, either at one time or at successive 

 positions, its edge occupied the Haverstraw and North Haverstraw 

 gravel plateaus. 



(3) The ice waters discharged into a standing body of water and 

 built up the deposits of gravel and sand, with the steep dipping 

 layers of gravel rapidly grading into sand and then into clay. The 

 clay was deposited on the irregular surface of the drift previously 

 deposited. 



Fig. 12. — Part of the Newburg delta, on the south side of the Quassaic. Looking 

 west. 



(4) The ice, either by re- advances, or because of more favorable 

 conditions in some places than in others while continually present, 

 worked over the clays, producing some of the contortions observed, 

 and involving masses of clay in the till which it deposited over the 

 clay in favorable places. The water-worn gravel was in places 

 brought under pressure, and the contact of the clay with the gravel 

 was thereby made more intimate. 



(5) On the retreat of the ice and the fall of the water-level the 

 higher-level gravels were eroded by the Minisceongo and Cedar 

 Pond Brook, thus producing deposits at lower levels. Whether there 

 are remnants of lower-level deltas cannot be confidently stated. They 

 would naturally be expected. 



(6) After deeper erosion by the streams than the present Hudson 

 level, submergence took place, thus drowning the mouths of the tribu- 

 tary streams. 



