Authors Abstracts. 



PAPERS READ AT THE MONTREAL MEETING OF THE 

 GEOLOGICAL SOCIETY OF AMERICA. 1 



Topography and Glacial Deposits of the Mohawk Valley. By Albert 

 Perry Brigham. 



The lower Mohawk, and a corresponding valley to the westward, are 

 considered as subsequent in character, having been initiated by head- 

 ward cutting from the ancient Hudson and St. Lawrence valleys, along 

 the strike of soft beds, to the col located by Chamberlin at Little 

 Falls. The Adirondack streams consequent on Palaeozoic topography 

 were thus diverted and the Susquehanna streams were beheaded. West 

 of Little Falls the rock floor descends toward Lake Ontario, but not 

 uniformly, a buried rock basin above ioo feet in depth, lying east of 

 Utica. The present arrangement is due to glacial and aqueo-glacial 

 erosion at Little Falls, and to aggrading from Rome eastward by 

 glacial materials. The westward flow of the lower Mohawk glacier is 

 confirmed by striation at Amsterdam. 



The drift deposits west of Little Falls are largely composed of del- 

 tas and benches whose altitudes indicate approximately a water level 

 of 600 feet. This is believed to represent a lacustrine stage in which 

 the waters had fallen below the Warren level and below Fairchild's 

 Geneva beach, but had not yet subsided to the Iroquois plane. The 

 dam is thought to have been at Little Falls, and of a composite nature 

 — the sill of gneiss then standing at about 440 feet, with drift and ice 

 blockade, in this long, sinuous, narrow gorge. Below Little Falls, mar- 

 ginal bodies of massive till, aggraded by water-laid material, show a 

 fluvio-lacustrine level of 430 to 440 feet, the barrier being unknown. 

 The next stage in the lower valley was also fluvio-lacustrine, at 340 

 feet. The gneiss then caused a great waterfall at Little Falls, and the 

 lacustrine stage persisted to the eastward, while a rock gorge more than 



1 Continued from last issue. 



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