POSTGLACIAL FEATURES OF THE UPPER HUDSON VALLEY 1 7 



the Upper Hudson valley. In this connection it is well to note that 

 the Hudson is today tidal water to Albany and Troy, but marine 

 life does not exist far above New York City. 



In the Hudson valley the land drainage always passed south, as at 

 present. During all the long time that the Labradorian ice sheet 

 lay on New York the enormous flood of the glacial melting was 

 added to the southward flow. This fact and its biologic effect does 

 not appear to have been sufficiently recognized. From a time 

 much earlier than the initiation of Lake Iroquois all the waters now 

 represented by the St Lawrence, and in addition the wastage of the 

 Labradorian ice cap, passed south through the Hudson valley, with 

 its constriction at the West Point highlands. And this flow lasted 

 until the waning glacier front receded from the high ground in Maine 

 and New Brunswick and permitted the St Lawrence gulf to unite 

 with the Champlain sea. Then the Hudson-Champlai n estuary became 

 the Hudson- Champlain strait, connecting the Gulf of St Lawrence 

 with the New York bay. Up to this time the flood of fresh water 

 was too great to allow marine life to pass up the Hudson. 



When broad connection was made between the Champlain interior 

 sea and the salt water of St Lawrence gulf a free circulation and 

 interchange was established and marine life entered the Champlain, 

 Ottawa and St Lawrence valleys. But this event had been long 

 delayed and in the meantime something else had happened. The 

 rising of the land, as it was relieved of the weight of the ice sheet, 

 had lifted the Hudson and Champlain areas so that the sea-level 

 waters then stood far below the initial shore line. 



In these facts of Pleistocene history we find a perfect explanation 

 of the absence of marine fossils from the earlier and higher deposits 

 of the sea-level waters, while they are abundant in the lower deposits 

 of the northern valleys. 



After the land on the Canadian boundary had lifted 215 feet there 

 seems to have been a much slower uplifting, or relative pause, which 

 produced the strong, close-set beaches about the north side of 

 Covey hill, with summit altitude of 525 feet. It is possible that 

 during this episode the salt-water life entered the Champlain valley. 



The question may yet be asked. Why did not the same marine 

 fauna found in the lower sand plains of the Champlain valley pass 

 south into the Hudson valley? There is satisfactory reply. The 

 land uplift was a wave movement progressive from south to north. 

 Uplifting had been in progress for a very long time in the Hudson 

 area before the Champlain area was much affected. By the time 



