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I12 NEW YORK STATE MUSEUM 
harmony with the rock structures and other drainage lines. The 
diversion from the preglacial course was due to heavy glacial accu- 
mulations between the villages of Black River and Evans Mills. 
The deep, narrow gorges which have been cut through the steep 
eastern and northeastern fronts of the Tug Hill plateau are com- 
monly called “ gulfs.” Of these the Whetstone gulf (see plate 8) 
is the most interesting and though little known it is one of the 
finest examples of its kind in the State. Its length is two miles, 
and for one mile it shows a depth of 300 feet. The walls are 
very steep-sided to nearly vertical, especially in the upper end 
(narrows) where there is just room enough for the swift stream 
at the bottom. This gulf is certainly postglacial in origin and has 
been cut into the soft Lorraine and Utica shales. During glacial 
times the shales were eroded back by the ice (see above) caus- 
ing the development of the steep eastern front of Tug hill. 
After the ice disappeared, all east-bound streams from Tug hill, 
not in their preglacial channels, rushed over the steep shale front 
and began to erode notches into its summit. These notches were 
rapidly deepened in the soft shales to form the gulfs whose heads 
have since been cut back to their present positions. 
The world famous Niagara Falls and gorge are wholly post- 
glacial in origin. After plunging 167 feet at the falls, the river 
rushes for 7 miles through the gorge whose depth is between 200 
and 300 feet (plates 47, 48, 49 and 50). When the glacial waters 
in the eastern Great Lakes region had dropped to the Iroquois level, 
the Niagara limestone terrace in the vicinity of Buffalo and with 
steep escarpment or northern front at Lewiston and Queenston, 
ceased to be covered by lake water, and the Niagara river came 
into existence by flowing northward over this limestone plain. The 
river first plunged over the escarpment at Lewiston and Queenston, 
thus inaugurating Niagara Falls there. Since that time the falls 
have receded the 7 miles up stream to their present position. In 
figure 38 we see that soft shales underlie the hard layer of Niagara 
limestone, and the recession of the falls has clearly been caused by 
the breaking off of blocks of limestone due to undermining of the 
soft shales. A glance at the map (plate 50) will show that the 
gorge development is really taking place on the Horseshoe falls 
side where the volume of water is much greater, and that in a 
short time, geologically considered, the American falls will be dry. 
The rocks exposed in the gorge walls are Niagara limestone, under 
which in regular order come Niagara (Rochester) shale, Clinton 
