NEW YORK STATE MUSEUM 



be no characteristics by which marine beaches as such can be dis- 

 criminated from lake beaches. As \yill be shown in more detail 

 in a report now in preparation on the whole question of the 

 marine invasion in the Champlain and Hudson valleys, certain 

 reasonable assumptions may be made with regard to the distri- 

 bution of beaches, by means of which, when the expectations are 

 met, the marine beaches in this area above the fossil shells and 

 below the level of the Gulf may be distinguished from those 

 made in glacial dammed lakes. In the first place, elevated 

 marine beaches may be expected to be traceable with more or less 

 continuity throughout the entire borders of low ground to which 

 the sea must have had access; the beaches may be expected to 

 succeed each other at any given place without very noticeable 

 breaks in the vertical succession, as a consequence of the rather 

 uniform nature of the elevation of the land above the sea. Glacial 

 lake beaches, on the contrary, would be expected to end where 

 they met the ice front, they should not therefore be continuous 

 where sea beaches would be continuous; the sudden lowering of a 

 glacial lake by the uncovering of a new outlet would cause notice- 

 able intervals in the vertical succession of these beaches; and par- 

 ticularly might an interval be expected between the lowest lake 

 beach level and the upper marine limit. 



There are other minor differences with regard to the develop 

 ment of lake and marine beaches which may be expected in the 

 Champlain district. In the making of marine beaches, the 

 strength of the wave action at any place depends in part on its 

 exposure, and that on the fetch of the winds across the water 

 body. Where the topography and materials to be wrought by 

 the waves are essentially the same from higher to lower levels 

 in a given portion of the area traversed by the regression of the 

 sea, a like strength of beaches is to be expected. 



In (he ease of deep waters along an ice front, the heavies! 

 wave action may be expected to occur independently of the con- 

 ditions which control normal marine waves. It will take place 

 at or near the junction of the shore line with the ice front; for 

 there the calving of the ice front in the production of icebergs 

 will sel up heavy waves, the force and direction of whose action 

 will be independent of the prevalent winds and the more remote 



