ANCIENT WATER LEVELS OF CHAMPLAIN-HUDSON VALLEYS 225 



what regularly deepened channel excavated in the drift filling 

 of the older rock gorge of the Hudson which it is to be pre- 

 sumed was quite as deeply filled when the ice began to retreat 

 as it now is. The most serious objection which I have to this 

 view is that it makes it necessary to suppose that the land 

 remained at practically the same level throughout the epoch of re- 

 treat and till the beginning of the marine invasion on the north. 

 If we accept, as on the whole seems necessary, the successive 

 deltas rising to the north from near the Narrows to beyond 

 the Highlands as indicating the actual water level within the 

 valley during that portion of the ice retreat, then two alter- 

 native hypotheses present themselves to account for the differ- 

 ence of inclination of the earlier and later levels in the lower 

 Hudson and Champlain valleys respectively. The first of these, 

 the simple one, attempts to explain the difference of inclination 

 by a more rapid rise on the north, not excluding, what the 

 observed facts demonstrate, some depression on the south. 

 Here again the fact that- the attempt is made to compare the 

 levels of water bodies which existed at very different times 

 leaves the matter in doubt. The second of these hypo- 

 theses is that after the retreat had gone on with bodies of 

 water standing in front of the ice with their levels approxi- 

 mately parallel owing to the stability of the land as regards 

 tilting, the whole eastern part of the State became tilted down 

 toward the north during the stage of Lake Vermont, and that 

 in the subsequent reversal of this movement the same district 

 participated blocklike in the change. There are no facts indi- 

 cating precisely how far above sea level any part of the district 

 lay, till the upper marine limit was established. For, though 

 we may determine the rate of tilting by a change of the former 

 sea level, it is obvious that the whole mass may have been 

 undergoing a positive or negative movement at the same time 

 that it was tilting. 



The district shows a number of features which are better 

 explained by this hypothesis than by the other view. In the first 

 place, the Albany clays sheet the rock terraces of the middle 

 and upper Hudson valley but are wanting over the Highland 

 and southern section, their lithologic equivalents being there 



