84 GLACIAL GKAVELS OP MAINE. 



with rather level top m the cross section. When traversing narrow valleys, 

 this plain appears like valley drift, but is distinguishable from it by the 

 very round shape of the pebbles, by its greater size than the valley drift of 

 the region, by the larger size of its stones, by the fact that it does not 

 always spread laterally to fill the valleys in which it is situated, and, still 

 more conclusively, by its going up and over hills. While crossing the 

 lower gi'ound the material is rather fine, approaching the top of hills it 

 becomes coarser, and on a steep down slope it is scanty or absent for a mile 

 or more. In Haynesville the osai'-plain proper is flanked by sand plains. 

 Apparently the osar was first deposited in a channel one-eighth to one- 

 foiu'tli of a mile wide. This was situated north of a hill 75 or 100 feet 

 high, and the water must have been at least of that depth in order to flow 

 southward over the hill. Subsequently this chamiel was widened by lateral 

 melting of the ice, until it became one-half mile or more wide and approxi- 

 mated the condition of a lake 75 or more feet deep. In this a plain of 

 fine sand was deposited at the flanks of the central plain of gravel. This 

 plain has subsequently been somewhat modified by the winds and by the 

 floods of the Mattawamkeag River, and to that extent is valley drift. No 

 30 miles of any other osar of eastern Maine at such a distance from the 

 coast has so great a cubic content as this series for the 30 miles north of 

 Danforth. 



Length, about 45 miles. 



ISLAND PALLS BRANCH. 



A nearly continuous osar extends from Merrill Plantation southward 

 near the line between Dyer Brook and Hersey to the village of Island 

 Falls, and thence southeastward along the western shore of Mattawamkeag 

 Lake and the west branch of the Mattawamkeag River, and joins the 

 Smyrna branch a short distance north of Haynesville. In some places, 

 especially toward the south, the gravel widens so as to approach the form 

 of the flat-topped osar-plain, but for most of the distance it takes the form 

 of a two-sided ridge with arched cross section. 



Since the Smyrna and the Island Falls tributaries are near each other 

 and are at equal distances from the sea, and penetrate regions having similar 

 rocks and topography, they throw light on each other's origin. The pebbles 

 are no rounder in the osar than in the osar-plain. The stones in both are 



