20 NEW YORK STATE MUSEUM 



town and Covey pass. On extensive delta plains with superabund- 

 ance of sand all beach features are wanting. Even where there 

 was considerable coarse material an abundance of sand appears to 

 have inhibited bar construction. It appears that wave work can 

 much more quickly pile cobble into ridges, but that sand requires 

 more time. The small sand bars that have been found were in 

 sheltered localities with weak iwave action. 



The combined deterrent effect of shifting water level, tidal fluc- 

 tuation, and dominance of sand or silt seems to be, in the light of 

 facts from other districts, sufficient explanation of the absence of 

 high-level beaches in the sandy areas along the sea coast. 



EXPLANATION OF MAPS AND DIAGRAMS 

 PLATES i-ii 



Plates I and 2. These maps are in coimpl'etion of the sieries of 

 maps showing the recession of the ice sheet over New York State, 

 published in New York State Museum Bulletin 160, plates 9-17. 

 Plate I shows the relation of the ice margin to the Iroquois and 

 marine waters during the second, and closing, stage of the glacial 

 Lake Iroquois, with the outflow at the pass on the international 

 boundary, on the south side of Covey hill. Lake Iroquois is here 

 at its greatest extension. 



In the earlier maps the waters in the Hudson- Champlain valley 

 were wrongly represented as glacial. This is now known to be an 

 error. The low attitude of the land at the time of the ice removal 

 permitted the oceanic waters to enter the great valley and per- 

 sistently lave the receding ice front. At the time represented in 

 these two maps the sea-level or estuarine waters had become con- 

 tracted, diminished in depth and width, in consequence of the 

 uplift of the land, which as a progressive wave had passed north- 

 ward, subsequent to the ice removal. Plate 3 shows the full amount 

 of the land submergence and the greatest extent of the sea-level 

 waters. 



In the Hudson valley it is probable that the land uplift never 

 overtook the retreating ice front ; but it is possible that some little 

 uplift occurred in the Champlain district while the ice had the 

 position indicated in plate i. The effect on the shore line will be 

 considered under plates 5, 10. 



Plate 2 represents the ice margin as removed from Covey hill, 

 thus allowing equality of level between the waters of the Cham- 

 plain and St Lawrence valleys. Lingering points of the ice lobes 

 are hypothetically depicted on the north edge of the map. 



