MODIFIED DRIFT ALONG SACO RIVER. 143 
the mile, flowing over modified drift. This consists of gravel and sand, 
and above the Rocky Branch these occupy an area one fourth to one half 
a mile wide, which lies mostly on the south side of the river, forming a 
nearly continuous interval 10 to 15 feet in height, which slopes with the 
stream, and irregular terraces which reach 25 feet higher. 
From the Glen station in Bartlett to Conway Corner the alluvial area 
averages fully a mile in width, lying in nearly equal amount on each side 
of the river. The greater portion of this is interval, from 10 to 20 feet 
in height, which is often seen to be composed of coarse gravel overlaid 
by fine silt, as on Androscoggin river. The flood-plain of the Champlain 
period is shown in the higher terraces of sand or fine gravel, 40 to 60 
feet above the river, which are nearly continuous on both sides. North 
Conway is built on a wide portion of the east terrace. The form of these 
terraces, with their surface level but usually narrow and bounded by steep 
escarpments, and their correspondence in height on opposite sides of the 
valley, make it easy to understand that a wide plain once reached across 
the intervening area. 
Along Seavey’s falls, which extend about a mile east from Conway 
Corner, the Saco is bordered on both sides by slopes of till and ledge. 
The modified drift of the highest terrace, however, is continuous between 
Pine and Rattlesnake hills, and thence extends two miles to the east on 
the north side of the river; and on the south it reaches from Conway 
Centre to the north-east side of Walker’s pond, and thence is nearly con- 
tinuous, though narrow, eastward to Maine line. East from the outlet of 
Walker’s pond, the interval between this terrace and the river on the 
south is not wide, but on the north it extends one half to one mile from 
the river, rising with a gentle slope to a height about 25 feet above it. 
On this side, the most elevated part of the alluvial area, as at Conway 
Street, is only a few feet above the reach of high water. The ancient 
flood-plain, which was from 40 to 50 feet above the present river, as 
shown by its terrace on the south, may have extended over this whole 
area, It would then appear that the river here began its excavation on 
the north side, and has been gradually cutting its channel deeper and 
deeper as it has slowly moved across this area southward. Remnants of 
the former high flood-plain are thus found at a nearly constant height 
above the river for fourteen miles, sloping in this distance more than 100 
