REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1902 r33 



rock prevented rapid down cutting, and, as the stream was 

 forced to cut laterally it migrated southward, denuding the 

 crystalline rock of its cover, either of rock or drift. The later 

 erosion was concentrated on the south side, and the crystallines 

 were finally trenched as we find them now. The earlier flow 

 must have had a great cascade over the fault cliff, and the map 

 contours in plate 13 show the wider valley below, headed by 

 an amphitheater, but the cliff has been worn to a slope as 

 shown in plate 24. 



A Uitudes 



For correlation with the lake and stream phenomena up the 

 valley, it is necessary to determine altitudes of the phases in 

 the down cutting of the rock barrier. The base of the Calci- 

 ferous on the north side, along Loomis street (the Dolgeville 

 road), the highest visible cutting, is 600 feet. The Archaean is 

 eroded into irregular benches, and near the city the lower 

 strong terrace, carrying Burwell street, is about 500 feet. 

 Eastern park, in the city on the south side of Burwell street, 

 and " Lovers Leap " on the south side of the gorge, are about 

 480 feet. The main part of the city is on the lower terraces, 

 from 500 down to 400 feet. Moss island is shown by the contours 

 as 400 feet. The New York Central station is 376 feet. The 

 river at the head of the rapids is 360 feet, and at the foot of 

 the rapids 320 feet. The principal overflow on the rock barrier 

 was at 500 to 400 feet. The more recent trenching is from about 

 400 feet downward. 



The amount of down cutting by the present river is relatively 

 small. In the western part of the city the broad plains, occupied 

 by buildings and the railroads, and undoubtedly the work of its 

 great predecessor, the Iromohawk, are only 15 or 20 feet over 

 the present waters. At the dams the water is not many feet 

 below the ancient rock platforms. The conclusion is that the 

 Mohawk has made only a narrow and shallow cut in the older 

 and broader channel, notwithstanding the fact, as pointed out 

 by Dr Gilbert, that it is a loaded stream, provided with cutting 

 tools. 



