FIFTH REPORT OF THE DIRECTOR I908 



19 



the central and eastern parts of the State two sheets of till are 

 indicated, one superimposed on the other. The indications are that 

 the later ice invasion was very weak. 



The southward overflow of the ice-impounded, waters held in 

 the Black river valley built high and broad deltas in the vicinity of 

 Trenton and Trenton Falls, and later north of Rome. During the 

 time of this overflow and earlier, glacial waters were also held in the 

 Mohawk valley much above the Iroquois level, and on the west and 

 south flanks of the Adirondacks above the Black river waters. The 

 existence of these high waters has been found to be due to the ice 

 blockade of the Mohawk valley. As the Labradoran ice sheet 

 waned and the Adirondack rock surface was exposed the On- 

 tarian ice lobe pushed eastward into the upper Mohawk valley 

 while the Hudson river lobe pushed westward up the same valley. 

 At an early stage of this opposing flow through the Mohawk valley 

 the westward flow of the Hudson lobe prevailed and excellent 

 drumlins were formed by westward moving ice, as far as Cedarville, 

 12 miles southeast of Utica. Professor Brigham has reported the 

 presence of west pointing drumlins in the Johnstown district. 



It is quite possible that the earliest waters which gathered in the 

 valleys of the Adirondacks found escape across the Mohawk glacier 

 to Susquehanna drainage. Certainly there came a time when an 

 open lake was held in the Mohawk valley between the two opposing 

 ice lobes. The earliest overflow of this Mohawk glacial lake seems 

 to have been across the col 6 miles east of Richfield Springs and 

 at the head of the Otsego valley, with present elevation of 1360 

 feet. The many broad delta plains at 1440 feet on the south flank 

 of the Adirondacks correlates with this outlet when allowance is 

 made for the postglacial deformation of the land. A lower escape 

 of the Mohawk lake was found at Cedarville at the head of the 

 Una d ilia valley, with altitude 1220 feet. This pass correlates with 

 the conspicuous sand plains at 1300 feet altitude. Possibly a still 

 lower escape was found at Bouckville to the Chenango valley at 

 1160 feet. But soon the overflow was shifted to the eastward by 

 the backing away of the ice front from the face of the Helderberg 

 scarp, 10 miles southwest of Schenectady. 



The Schoharie valley had held glacial waters (as shown by 

 Professor Brigham in my last report) with earliest outlet by one or 

 more of the three passes at the head of the basin, at 1920 feet. 

 Later the Schoharie waters blended with the Mohawk waters with 

 overflow by the outlets leading to Susquehanna drainage, as noted 

 above. The pass at 1500 feet to the Schenevus valley never carried 

 any flood. The pass south of Middleburg to the Cat skill creek. 



