40 



NEW YORK STATE MUSEUM 



southward to the southern limits of the map, beach ridges rib the 

 slope at Sciota from 495 feet down to 250 feet according to the 

 contours of the map. Beach ridges and waterworn gravels occur 

 either side of the state road from Sciota to the vicinity of Tracy 

 brook. At 450 feet Bovington brook, as noted by Dr Gil- 

 bert, cuts through a well formed bar with a typical under w^ater 

 beach slope in front of ; the bar. Above this level along the 

 road to Cobblestone hill there are faint parallel lines with 

 rather angular washed material indicative of wave action at 

 530, 545 and 580 feet (by the map). These higher water lines 

 are apparently traces of the water body which sank stage by 

 stage from the, 570 foot level in this latitude to the lower series 

 of beaches. South of West Chazy stronger and broader bars 

 than appear on the north come into existence in a slightly 

 overlapping or offset arrangement, which is fairly well shown 

 by the contouring of the map just above the 420 foot line. 

 These broader ridges are marked by minor beach ridges. East 

 of West Beekmantown, these larger bars take on the form of 

 definite offshore bars, inclosing back swamps. Silver creek 

 winds its way in rectangular adjustment down the slope run- 

 ning part way between the bars and part way transverse to 

 their extension where they become depressed and exhibit their 

 offsetting. Another broad wave-heaped ridge of this character 

 occurs south of West Beekmantown at about 500 foot eleva- 

 tion. West of this beach wave marks appear at about 545 feet. 

 There is a distinct group of half a dozen beach ribs on the 

 slope south of Silver creek from 315 feet up to 340 feet. This 

 group of minor beach ridges extends northward and merges 

 into the broader belt of greater vertical range north of West 

 Chazy. 



The beaches of this lower series, as a whole, are composed of 

 highly angular materials, often flat slabs of Potsdam sandstone 

 or angular polygonal blocks dependent apparently on the man- 

 ner of fracture of the nearby underlying Potsdam sandstone 

 derived either from ledges or the glacial drift worked over by the 

 waves. In the northern part of the map near the international 

 boundary, rolled and rounded pebbles aside from those in the 

 deltas near streams as at 420 feet east of the English river, first 

 appear at an elevation of about 350 feet on the western slope of a 



