ANCIENT WATER LEVELS OP CHAMPLAIN-HUDSON VALLEYS 131 



ward at the brink of the gorge is now 200 feet. The surfaces 

 rise northwestward to an elevation of about 350 feet near Schenec- 

 tady. Between Schenectady and Albany the surface is mantled 

 with extensive dunes of fine sand whose elevation rises to 400 feet, 

 causing a postglacial elevation of the surface in this district by 

 accumulation at the expense of the elevation of the deposit farther 

 west near Schenectady. The Mohawk river now flows on the 

 north of this delta. As will be noted in the account of the 

 region north of the river the delta appears not to have been de- 

 posited in that district for the reason that it was covered by ice 

 at the time the delta was building. 



The present course of the Mohawk from Schenectady eastward 

 is in a rock gorge separated, along the northern border of the 

 town of Mskayuna, from the delta plain by till-covered ground 

 rising above the delta level. At Alplaus^ the Ballston channel 

 extends to the north and east. The history of this network of 

 drainage lines including the Ballston channel, and the Round 

 lake drainage, has not been fully investigated. It seems clear 

 however that the Mohawk delta began to make when the retreat 

 of the ice sheet opened a passageway along the area covered by 

 this deposit, and that the waters coming through the Mohawk 

 valley pursued this course while the delta was building. At a 

 later time when the ice melted away from the northern border 

 of Niskayuna it left a tract at a lower level than the surface of 

 the delta on the south and the river naturally began to flow 

 along the course it now pursues below Schenectady. 



It is difficult to fix any definite water level by the present eleva- 

 tion of the Mohawk delta. Certainly its lower clayey border near 

 the Hudson river was under water during the stage of deposition. 

 Presumably its upper stretches were not under water except in 

 floods. 



From a comparison of the neighboring evidences of shore lines 

 indicated by small deltas and the upper limit of clays, I have 

 hesitated to place the average water level above 320 feet. 



Summary of the Newburg and related stages. Though the 

 western border of the glacier which lay in the mid^ile Hudson 

 valley between Albany and Newburg has not been definitely 



iThis is the present corrupted spelling of the place originally called 

 Aalplaatz — a good place for eels. 



