462 F. J. II. Merrill— Post- Glacial History 



75th street northward have a maximum height of 70 to 75 feet 

 and on the Xew Jersey shore of the river, terraces of about 

 the same altitude occur at frequent intervals. One of the most 

 prominent of these is at Fort Lee, south of the steamboat 

 landing. The surface material of these terraces is a fine sand 

 or silt easily transported by the wind. It is evidently not a 

 material which could be laid down in running water, for it 

 would be carried in suspension by a river current and could 

 only be precipitated in the still water of an estuary. Xorth of 

 New York City the altitudes of the terraces have been deter- 

 mined at a few points as follows : 



Mouth of Croton River 100 feet. 



Peekskill 120 " 



West Point 180 " 



Fishkill 210 " 



Schenectady 340 " 



A detailed measurement of the terrace altitudes between 

 Fishkill and Schenectady has not yet been made. 



On the Long Island Sound shore of Westchester County, ~N. 

 Y., the till which covers the metamorphic rocks has apparently 

 been levelled off by wave action at an altitude of 75 to 85 feet. 

 Plains of this character occur at frequent intervals, being 

 separated by river valleys, and were probably formed during 

 the depression which occasioned the estuary deposits of the 

 Hudson River valley. These plains are composed of a modified 

 till, obscurely stratified, somewhat sandy near the surface and 

 comparatively free from bowlders, but unaltered bowlder clay 

 or till occurs at a few feet below their surface. On one of the 

 most extensive of them the village of Xew Rochelle has been 

 built. 



On Staten Island and western Long Island alluvial plains of 

 stratified material rise gently from the ocean shore to the mar- 

 gin of the moraine, terminating at an altitude of about 80 feet, 

 and, though no continuous shore-line is to be found, the plains 

 are referred provisionally to the same period as the estuary 

 deposits a few miles north. 



From the evidence quoted the amount of the post-glacial 

 depression at Xew York is estimated at about 80 feet. 

 Whether this was subsequent to a greater depression of post- 

 glacial date remains to be determined. 



In the estuary which occupied the Hudson Piver valley 

 during the depression, there was deposited a great depth of plastic 

 clay, evidently a sediment of aluminous rock flour produced 

 by glacial attrition, and held in suspension by the post-glacial 

 streams, and resting upon this clay, is a deposit of fine stratified 

 sand. This bipartite character of the Hudson Eiver estuary 



