.CK AND MOHAWK VALLEYS 33 



arable to the St Lawrence. It seems prob- 

 .iiy endured to the close of Iroquois time. 

 ■ .cnts and deformation. The present river from 

 u feet) to Schenectady (210 feet) falls 210 feet in 92 

 jy the ime of the valley (not counting the stream meanders), 

 .nch gives 2.3 feet per mile. The actual slope of the river is much 

 less above Herkimer. At and below Schenectady the river has 

 intrenched itself about 130 feet below the head of its ancient delta, 

 the Lake Albany plane. The Iromohawk river must have poured its 

 flood across the delta, now 340 feet in elevation at -South Sche- 

 nectady. The col at Rome is now 430 feet. From this we must 

 deduct about 55 feet for 2y miles of northing, making 375 feet the 

 altitude of the head of the later Iromohawk channel. This gives a 

 fall of 35 feet in 92 miles, or a gradient of 0.38 feet per mile. The 

 elevation of the highest wave-built bars and spits in the Iroquois 

 basin near Rome is 460 feet (see plate 2),^ which gives 30 feet of 

 water over the sill of the channel head, which is a normal depth for 

 the great river. If we allow the same depth of water at the mouth 

 of the river, and the South Schenectady deposits are fine, indicating 

 submergence, we have the same moderate grade as for the channel 

 bottom. These figures accord well with the grade of large rivers 

 and indicate that our estimate of the deformation is fairly correct. 

 In the comparison of channels and lake plains in central New 

 York and the Mohawk valley we find the northward uplift to be 

 about 2 feet per mile,' perhaps a trifle more. Hence if we allow 

 this amount of uplift on the Rome meridian there is no balance left 

 for east and west deformation. It is positive that through central 

 New York, from Sodus to Rome, there is no appreciable east-west 

 tilting since Iroquois time,^ and it seems quite certain that the 

 uniformity extends east to the Hudson ; in other words, that the 

 isobasal lines have here approximately east and west direction. 



TRIBUTARY LAKES 



Besides the Black valley waters which during most of their life 

 were tributary to the Mohawk waters, as already described, other 

 lakes were held at high levels along the margins of the ice lobes and 

 found escape into the Mohawk. The lakes held in the valleys 

 between Syracuse and Utica were described in the Twenty-second 



1 The writer is indebted to Mr F. B. Taylor for first drawing attention 

 to these features. 



2 See N. Y. State Bui. 127, p. 55. 



