102 J. D. Dana on the origin of some of the 



methods than by tlie use of a hand-level, ordinary measurements of 

 the heights of dams, and estimates only of the slope of back water. 



In the West River valley, the depth of the excavation made by the 

 river is 45 to 48 feet in its lower part just above the limit reached by 

 the tides, or near the Whalley Avenue bridge ; but \\ miles (in an 

 air-line) up the valley, neai- the Pond Lily Paper Mill and beyond, 

 it is only 7 or 8 feet. The river therefore, to within 1^ miles of the 

 tidal limit, has a level hut "J or S feet helow that wJiich it had in the 

 ChanqylfU'in era. The plain spreads across this part of the valley and 

 stretches far northward. But although showing so little elevation, it is 

 actually over 10 feet above mean-tide level. The river has a descent of 

 72 or 73 feet from the head of back-water of the Pond Ijily dam to 

 the bridge, a distance of Ij miles, in an air-line, which is equivalent 

 nearly to 54 feet a mile.* There is also an unusually high angle of 

 slope in the terrace plain of the valley, its height a mile and a half 

 (1*50 m.) up the valley, being about 82 feet above mean-tide level; 

 at 1*15 m. (Pond Lily dam), 72 feet; at 0-62 miles (below Parker's 

 Paper Mill), 62 feet; at 0-3 miles (near the Congregational church), 

 56 feet ; or in all about 24 feet a mile. These striking peculiarities of 

 West river, may come partly from the valley being comparatively 

 narrow ; but they arise mainly from the fact that the terminating 

 ridge of the Edgewood line of hills crosses the course oi% the 

 stream just below the Pond Lily Paper Mill, and the passage cut 

 through it for the waters is shallow. The bed of the stream in this 

 part, as through all the region of rapids below, is made up of large 

 boulders, and none of the scliistose rocks of the Edgewood range are 

 in sight ; but they must lie not far below. The terrace plain, standing 



* The falls above the Whalley Avenue bridge are as follows : 1st dam, 4-J- feet ; 2d or 

 Beecher's dam, 8 feet ; between 1st and 2d dams, 1 foot ; 3d dam, or Mallory's, 9 feet ; 

 above Mallory's, (Parker's and the Pond Lily dams), 50 feet; in all, 72^ feet. The 

 terrace near Beecher's dam is 42 feet above the level of the pond, and the pond is at 

 surface 13^ or 14 feet above mean-tide level. The average course of the river from the 

 bridge northward is about northeast, so that in 1^ m. in its direction there is only about 

 1 m. of northing. 



I may add here, as an addendum to page 76, that just west of the Whalley avenue 

 bridge, the oblique lamination in some of the layers of the terrace formation indicates 

 the existence of a great river flood, or current southward, during the deposition ; like 

 that which existed, according to similar evidence, in the Quinnipiac. But east of the 

 bridge, the obhque lamination has the reverse dip, and thus shows that, throughout 

 the progress of the deposition quite to its close, the sands were under the action of 

 waves and tidel currents from the bay and not that of the river currents. This region 

 east of the bridge, as the map shows, is outside of the Westville valley, the river bend- 

 ing in this part quite far to the eastward. 



