210 BRIGHAM—TOPOGRAPHY AND DEPOSITS OF MOHAWK VALLEY. 
then standing at about 440 feet, with drift and ice blockade in the long, 
sinuous, narrow gorge. Below Little Falls marginal bodies of massive 
till, aggraded by water-laid material, show a fluvio-lacustrine level of 
430 1o 440 feet, the barrier being unknown. The next stage in the lower 
valley was also fluvio-lacustrine at 340 feet. he gneiss then caused a 
great waterfall at Little Falls, and the lacustrine stage persisted to the 
eastward, while a rock gorge more than 100 feet deep was cut at Aque- 
duct near Schenectady. Certain beds of massive water-Jaid clay west of 
Little Falls, taken with similar deposits in the Chenango and Unadilla 
valleys, are thought to show long and quiet deposition, with perhaps 
considerable later erosion before the last advance of the ice across central 
and southern New York. 
