4<) NEW YORK STATE MUSEUM 



Accepting the evidence at Covey hill for placing the upper marine 

 limit at 450 feet, it would further appear that the beaches in 

 this region above that level are those of a glacial lake. The 

 evidence found in the southern part of the Plattsburg quad- 

 rangle about Port Kent seems to indicate that the upper marine 

 limit is there to be placed at an elevation not more than 330 

 feet above sea level of today. On this basis plate 25 has been 

 prepared exhibiting the shore line as it is presumed to have 

 stood at the time the sea was at its maximum extension in the 

 Champlain valley. This line it will be noted makes an arbitrary 

 division of the crowded beach lines in the lower series. 



As stated in another place the marine shells which occur near 

 Mooers at 340 feet, and on the Saranac above Plattsburg at 

 aj : proximately the same elevation, 342 to 346 feet, prove that the 

 sea stood as high as 340 feet at least over the northern part of the 

 district. It is to be presumed that shells may be found as high as 

 the marine limit in beach deposits. As yet shells have not been 

 reported in the beaches of this district. 



The upper marine limit as here placed coincides with a tilted 

 plane passing through the 450 foot beach at Covey hill and 

 just above the 550 foot marine shell deposit on Mt Koyal. 

 This plane intersects the delta of the Big Chazy at Mooers 

 Forks, and the heavy beaches south of Sciota [pi. 18-21] at about 

 400 feet; it also passes beneath the rock cliffs from the waste of 

 which these beaches are in part built [see pi. 22-24] . 



Marine invasion 

 It has long been known that on the disappearance of the ice 

 sheet from the St Lawrence and Champlain valleys the sea cov- 

 ered the floors of these valleys at least as high as the localities 

 at which marine shells have been found in the clays and sands 

 laid down at that time. Opinion has differed among geologists 

 only as to the depth to which the land in various parts of this 

 portion of the continent was then submerged. The character 

 of the fossil shells, the fact that many of the species are 

 still living in the St Lawrence gulf or in the adjacent waters 

 of the Atlantic coast show that these animals found their way 

 into the Champlain valley from the north or northeast. The 



