ANCIENT WATER LEVELS OF CHAMPLAIN-HUDSON VALLEYS 201 



Chapter 10 

 THE MAEINE INVASION 



It has long been well known that as the Wisconsin ice sheet 

 disappeared from the margin of its gathering grounds in Ungava, 

 the sea at once covered large tracts about the shores of Hudson 

 Bay, throughout the St Lawrence valley, along the coast of New 

 Brunswick, Maine and New Hampshire, and probably also a narrow 

 strip of the coast of Massachusetts north of Boston. The main 

 geologic problem awaiting solution in these fields is that of deter- 

 mining the upper marine limit. The literature of the field 

 presents the greatest variety of opinion on this subject, the vertical 

 and horizontal range of the marine waters being limited by each 

 writer according to very different criteria. While the earlier 

 writers as a rule were inclined to regard the submergence as of 

 great depth and wide extent, recent investigators exercising a 

 closer and more cautious discrimination between the effects of 

 glacial waters, lake waters and those of the sea have tended to 

 restrict the submergence to narrower limits. As will be observed 

 I have come to an essential agreement with Baldwin^ whose paper 

 on the Champlain district has the merit of including a diagnosis 

 of the marine limit on the Vermont side of the valley. 



THE UPPER MARINE LIMIT 



The criteria appealed to by different geologic writers in the 

 establishment of the upper marine limit in this part of North 

 America indicates a wide diversity of opinion as to the effects of 

 marine action and consequently as to the extent of the postglacial 

 submergence in this district. All are agreed that the upper limit 

 of marine fossils is a trustworthy though probably a minimum 

 measure of the vertical extent of the submergence. Most geolo- 

 gists would probably also accede to the zoologic postulate that the 

 marine limit does not lie higher above the shell line than the depth 

 of water indicated by the fossils as necessary for their growth. 

 Such is the present vertical range of most of the species found in 

 the Champlain valley — 100 to 300 feet — that they do not furnish a 

 criterion for discriminating between marine beaches and glacial 



^Baldwin, S. P. 1894. See bibliography, 1. 



