ALLUVIAL TERRACES OF SAGO RIVER. 255 



of this series, without having to rise over hills higher than 100 feet, measured 

 on their northern slojjes. 



ALLUVIAL TEBRACES OF THE SACO RIVBR. 



From the sea to near Bonny Eagle, in Standish, the Saco River is bor- 

 dered by terraces of erosion in the marine beds. Near the river these 

 marine sediments differ but little from those found at a distance from the 

 river. If the ice had melted before the marine beds were laid down and 

 the sea advanced, the river would have begun to flow before the deposition 

 of the clays, and we should now find a plain of valley drift overlain by the 

 marine beds The fact that these beds are substantially the same near and 

 far away from the river valleys shows that the rivers had not began to flow 

 at the time of their deposition, and that they were a rather deep-water 

 formation. 



Near Bonny Eagle the Saco enters the great marine deltas brought 

 down by the glacial rivers, overlain b}' the delta of the river after the melt- 

 ing of the ice That the glacial deltas were deposited in the open sea is 

 proved by the fact that they are confluent and practically continuous over 

 a broad area extending from Standish southwestward through Limington, 

 Hollis, Lyman, Waterboro, Alfred, and Sanford, to Noi'th Berwick. For a 

 few miles above Bonny Eagle the erosion terraces of the Saco are exca- 

 vated in sand overlying clay. Then the gravel appears, and above Steep 

 Falls coarse gravel, cobbles, bowlderets, and some bowlders form a large 

 part of the river terraces. Where there are broad plains of porous gravel 

 bordering the river there is usually more erosion than in the narrow parts 

 of the valley This is due largely to the action of subterranean waters in 

 the manner elsewhere described. 



North of Hiram lie a number of broad, rather level valleys opening 

 southward. This would tend to converge the ice into the narrower valley 

 of the Saco extending from this point south and east. Late in the Ice 

 period as the ice retreated there would naturally be a local glacier in the 

 valley, i e., one following the valley independently of the previous general 

 movement. It is a difficult problem now to determine how much of the 

 deep sheet of water-assorted matter that covers the Saco Valley from 

 Hiram to Steep Falls was deposited during the general movement and how 

 much was the work of the more local glacier. As the ice retreated up the 



