GLACIAL WATERS IN BLACK AND MOHAWK VALLEYS I3 



a prominent feature of the Port Ley den quadrangle (see page 15) 

 are wanting in the Forestport sand plains. 



These sand plains seem to have been built against or near the ice 

 margin, and the materials are theoretically of triple origin : largely 

 detritus brought in by the Adirondack drainage; partly contributed 

 by streams pouring out of the melting glacier ; and partly derived 

 from the wave erosion of the kames and glacial deposits. 



The Forestport sand plains lie in a series of sloping terraces, 

 decHning westward. Five miles northeast of Forestport, on the north 

 edge of the Remsen sheet, the highest plain is 1400 feet, though 

 there are evidences of wavework still higher. Other terraces or 

 benches of the district are found at all levels down to 1140, the 

 terrace on which the village stands. Near Enos, six miles southeast 

 of Forestport, are sand plains at 1420 down to 1360 feet. The levels 

 above 1300 feet must certainly belong to the first stage, or Mohawk 

 waters, while those below 1200 feet as certainly belong to the next 

 and lower stage. Port Leyden lake. It will not be possible to 

 correlate all the terraces with definite attitudes of the waters, and 

 the tilting of the land complicates the study. But this fact is 

 brought out clearly, that the sand plains were spread out in slowly 

 subsiding waters and were extended westward at lower and lower 

 levels as the ice front receded. 



On the map (plate 2) the delta plains credited to the several lake 

 stages are indicated by different shadings (" conventions ") and the 

 limits can not be exact. The altitudes of the upper and lower limits 

 of the Forestport lake deposits are taken as about 1280 and 1200 

 feet. As a rule the shadings are restricted to terrace limits, but it 

 is possible that some higher portions of sand plains marked as 

 P'orestport may belong to the earlier Herkimer lake, or that some of 

 the lower parts may be deposits of the subsequent Port Leyden 

 waters. However, in a general way the map must indicate the true 

 relations. 



These plains have been noted by W. J. Miller (see title 27, 

 pages 42-45)- 



In the maps showing the waning of the ice sheet the Forestport 

 lake is not indicated, but it belongs to a phase between those of 

 plates 13 and 14. 



THIRD STAGE : PORT LEYDEN LAKE ; BOONVILLE OUTLET 



This lake is the one of longest duration in the life of the Black 

 valley glacial waters. Its outlet was the narrow, deep gorge of the 

 present Lansing kill, extending from Boonville south some 10 miles 



