O NEW YORK STATE MUSEUM 



A concise outline of the history described in the following writing 

 will be helpful to the reader. As the large physiographic relief we 

 have the elevated tract of the Adirondacks surrounded by low and 

 broad valleys ; the Champlain-Hudson on the east, the Mohawk on 

 the south, the Ontario on the southwest and west, and the St Law- 

 rence on the northwest and north. The highest point in all this ring 

 of lowland is the col at Rome, about 430 feet above tide, the head 

 of the Mohawk valley which is the connecting channel between the 

 Ontario and Hudson valleys. 



As the Labradorian ice body, which had at its maximum covered 

 practically the entire State, waned and lost in thickness the Adiron- 

 dack heights appeared above the ice field, standing as an island in 

 the ice sheet, although local or stream glaciers probably occupied 

 for a time some of the higher valleys. The high Catskill-Helderberg 

 mass must have already been deserted by the ice sheet, and conse- 

 quently there was left a strait or neck of ice in the Mohawk valley 

 connecting the Ontarian and Hudsonian ice lobes. This stage in the 

 ice retreat is shown in plate 12. 



The removal of the ice was partly by evaporation but chiefly by 

 melting and water must have collected about the base of the Adiron- 

 dack island, forming a chain of lakes in the depressions. This 

 water would fill all the crevasses in the ice margin and to some 

 extent would penetrate in and beneath the shallower ice, but it is not 

 believed possible for the water to have found escape through or 

 beneath the deep ice which lay in the Ontario and Hudson valleys. 

 Its only possible ultimate escape must have been over and across the 

 strait of ice south of the Adirondacks. Some of the extensive sand 

 plains, even in the heart of the mountains and with altitude over 

 1400 feet, must belong to this episode in the drainage. 



With the continued waning of the ice body the neck of ice in the 

 Mohawk valley was melted away and was supplanted by a lake held 

 between the two opposing ice lobes, the Hudsonian lobe pushing up 

 the Mohawk valley from the east and the Ontarian lobe blocking 

 the valley on the west. This stage is shown in plates 13-15. 



The Mohawk glacial waters were lowered and finally extinguished 

 by the weakening and recession of the Hudsonian ice in the vicinity 

 of Schenectady (see plates 14-16). 



Contemporary with the Mohawk glacial waters were waters held 

 in the valley of the Black river by the ice blockade on the north, 

 with earlier outflow southward into the Mohawk lakes. The later 

 escape of the Black waters was westward into Lake Iroquois, in the 

 vicinity of Copenhagen and Carthage (see plate 17). 



