82 GLACIAL GEAYELS OF MAINE. 



Excavations not in the dunes show the sand overlying the till and till 

 bowlders. This bordering sand plain has the external features of valley 

 drift. At the gi'eat bend, or "oxbow," of the Mattawanikeag the river 

 makes an abrupt turn from a southeast to a southwest course. The osar- 

 plain here leaves the river valley and goes on southward through Weston 

 to Danforth. The character of the alluvium of the Mattawamkeag Valley 

 here changes. Below this point the river shows an alternation of long 

 reaches of dead water separated by short rapids or falls. Along the level 

 parts of the valley the river drift consists of clay and silt, with sand, sub- 

 angular coarse gravel, and even bowlderets and bowlders at the rapids. 

 The rapids are found at places where the ice-sheet left deep masses of till 

 spread across the valley. The only gravel found in the valley below the 

 oxbow is the result of the river's eroding the till, and the shapes of the 

 stones are very difiPerent from those of the osar-plain in Haynesville. 

 True, some rounded stones can be found in the bed of the river, or as a 

 part of the lowest terrace, for some miles below the oxbow, but they were 

 probably washed down from the osar-plain, although I could not prove them 

 to be contemporaneous with it or with any of the higher terraces. The till 

 ridges left across the valley of the Mattawamkeag must originally have 

 caused a series of lakes to form in the valley directly after the melting of 

 the ice. The broad sand plain found boi'dering the osar-plain proper in 

 Haynesville might thus be a lake delta if a till iDarrier high enough to form 

 a lake at that level existed. Thus far I have found no barrier high enough 

 for the purpose. Concerning the broad plains of the Mattawamkeag 

 Valley extending from Haynesville to the oxbow, it is safe to conclude, 

 first, that the sand-and-gravel plain near the center of the valley is a true 

 osar-plain; second, that the bordering plain of sand was probably deposited 

 in a still broader channel within the ice, making it in fact a glacial lake; 

 yet there is nothing in its form to disprove the hypothesis that it was formed 

 in an ordinary lake if a till barrier (now cut through by the river) of suffi- 

 cient height can be found; or it may possibly be an overwash or frontal 

 plain deposited when the ice had retreated a little north of Haynesville. 



A plain of sand and fine gravel extends from the great bend of the 

 Mattawamkeag southward through Weston. It is one-eighth of a mile or 

 more wide, and ascends the valley of a small brook which flows northward. 

 The stream has excavated numerous terraces of erosion in the osar-plain. 



