Topographical Features of the New Haven region. 101 



per mile for the rise in the back-water above the clams, and as mxich 

 more for descent above Augurville not included in the falls of the 

 dams, is as follows at the diiferent points here mentioned : — 



2^ m. north of Whitneyville, below the Augurville dam 36 feet. 

 4 m. N. of Whitneyville, ~h m. S. of Ives's Station - 60 " 

 5^ m. N. of Whitneyville, below the Mt. Carmel dam 80 " 

 6 m, N. of Whitneyville, above the Mt. Carmel dam 92 " 



It follows from the facts that the present slope of the bed of the 

 river is about 15 feet a mile, while that of the terrace plain or old 

 flood grounds varies from 13 to 9 feet a mile. The latter was the de- 

 scent of the river in the Champlain era; and consequently the e - 

 cavation which has taken place since the elevation closing that era 

 has not wrought out as gradual a descent as the earlier, by one to five 

 feet a mile, 1 foot a mile of the slope being taken as a result of an ele- 

 vation of the land (p. 98, §4). 



The height of the terrace corresponding to the line of the Whitney- 

 ville dam being 55 feet above mean-tide level (p. 95), its height above 

 the surface of the river as it stood before the dam was built would bq 

 about 53 feet. Consequently, the amount of excavation that would 

 be required at Augurville to restore the old slope would be 3 feet (50 

 feet being the height of the terrace above the rivei'^s surface) at Ives' 

 StaMon, 12 feet; below the Mt. Carmel gap, 5;^ miles from Whitney- 

 ville, 1 7 feet ; below the dam at the gap, 5^ miles from Whitneyville 

 (where the terrace as deduced from the average slope in this part of 

 the valley has a height of about 34 feet above the river's surface, 

 though now abnormally lower), 19 feet. 



At the Mt. Carmel gap there is a descent of 12 feet in half a mile, 

 owing to the hard trap rock lying in the way of the I'iver ; but the 

 terrace plain above appears to correspond in level with that below, 

 that is, it has nearly the same slope and is almost in the same con- 

 tinuous plain. For while the river here descends 12 feet in half a 

 mile, the depth of the cut made by the river through the terrace or 

 drift formation north of the gap is only 26 feet — this being the heio-ht 

 of the terrace plain above the river. The amount of excavation in 

 this part of the valley would therefore have to be 27 feet. 



These numbers, as already observed, are only approximations. For 

 exact results, the slope of the bed of the river and the heiglits and 

 slope of the terrace plain should be ascertained by more accurate 



F. Ives's dam, 12 feet; between the last two, 8 feet; in all 89 feet. The back-water 

 of F. Ives's dam is less than a fourth of a mile in length, and its head about 6 miles in 

 an air-line north of Whitneyville. 



