GLACIAL AND POST-GLACIAL HISTORY 461 



Fossils. — Below the upper terrace of the lower series of terraces 

 marine fossils occur on the west side of Lake Champlain at the fol- 

 lowing elevations: Plattsburg, 346 feet A. T.;' Port Douglas, 300 

 feet A. T.; Willsboro, 200 feet A. T.; Port Henry, 140 feet A. T. 

 So far as the writer knows, the last-mentioned place is the most 

 southerly point where marine fossils have actually been found. 



At South Plattsburg both marine shells and vegetation are found 

 in a deposit of sand and silt, the top of which has an elevation of 220 

 feet. 



SALMON RIVER SECTION, NEAR SOUTH PLATTSBURG.^ 



15. Silt.. 



14. Ten feet of coarse gravel, with ridge topography. The sand below the 

 gravel ridges is eroded and replaced by coarse gravel, largely of Potsdam 

 sandstone, but some light-colored limestone. Shells in single valves. One 

 square-shouldered valve found. 

 13. Six feet of sand (and gravel ?), some stratified; single valves of round-shoul- 

 dered shells. 

 12. Fifteen to twelve feet of sand and silt with round shouldered-shells in the sand. 

 1 1 . Eight feet of coarse sand; shells rare — only one found. 



10. Two feet of fine sand, a three-inch layer with occasional round-shouldered 

 shells (valves together). 

 9. Clay and sand; a four-inch log, two inches from the bottom of the layer; 



shells rare. 

 8. Shells and vegetation. 



7. Two feet two inches of alternating sand and clay. 



6. Layer of vegetation one-half an inch thick, with a fragment of a beetle. 

 5. One foot of sand. 



4. Two feet nine inches of sandy clay; no shells, but vegetation marks. 

 3. Blue clay; square-shouldered shells in sandy seam with specks of vegetation 



four feet above the river. 

 2. Till; stony material, largely limestone; some purple quartzite. 

 I. Rock. 



The layers of sand and silt are much contorted near the surface, 

 and again not far from the base of the section. The dip is eastward 

 .at a low angle. Just a little farther downstream there are several 



1 Dr. D. S. Kellogg, Science, June 17, 1892, p. 341. 



2 The material found in this section has not been fully identified but is being 

 studied. Leaves in layer 6 have been identified by Professor J. M. Coulter as 

 belonging to some species of boreal willow. The square-shouldered shells are prob- 

 .ably Saxacara rugosa and the round-shouldered shells are Tellina Groenlandica. 



