MODIFIED DRIFT ALONG SACO RIVER. I43 



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 lo 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 



