155 NEW YORK STATE MUSEUM 



body of water at that time. Subsequently, it has been cut off and 

 isolated by Putnam's creek. 



Whatever the nature of these inland waters, marine or glacial, 

 it is certain that they remained at a definite level for a long period 

 of time, then dropped quickly to a lower level, at which they 

 remained for another long period, and that this was repeated several 

 times. Had the region been occupied continuously by an inlet 

 from the sea, as postulated by Fairchild, and had the surface of this 

 inlet stood always at sea level, the present altitude of the ancient 

 shore lines could be accounted for only by subsequent elevation of 

 the land. This elevation must have occurred, then, at irregular 

 intervals instead of steadily. The land must have remained sta- 

 tionary at each period when a well-marked shore line was formed, 

 and must have risen rapidly during the intervening intervals that are 

 not marked by well-defined shore line phenomena. Elevation at 

 the north must have tilted the waters gradually from the north end 

 of the valley southward. The land must have risen as far south 

 as New York harbor in order to convert the bottom of the inlet into 

 dry land. All evidence, however, shows that the reverse of these 

 conditions prevailed here; and that the lower Hudson has sunken 

 since glacial times and is still sinking. 



Woodworth has adduced good evidence for the continued stand 

 of a glacial lake at each of these levels. He has shown that the 

 wearing down of outlets to the south has several times resulted 

 in lowering the level of the glacial lake ; that a final retreat of the 

 ice from the northern end of the valley allowed marine waters to 

 enter from the north. This stage, and this stage only, is recorded 

 by fossil remains. They are all of marine nature. 



EROSION 



Since the marine waters left the embayment, or rather, since 

 the land has risen in its relation to the sea, Putnam's creek has 

 done a large amount of valley cutting. It has not only continued 

 with its tributaries to. dissect the uplands that form the old lake 

 beds, and which it had begun to cut through during the marine 

 occupation, but it has divided the marine delta into two parts and 

 has removed fully one-third of it from the central portion. It has 

 excavated here from the i8o foot delta surface down to a base level 

 that was once, probably, below the present level of Lake Qiamplain, 

 as will be explained presently. During this process of degradation 

 the creek meandered from side to side widening and cutting down 



