SEBOOIS-KINGMAIsr-OOLUMBIA SYSTEM. 99 



The ridges were thus flanked on each side by a stream. About 30 feet 

 below the dam these two ridges were connected by a transverse ridge, thus 

 inclosing a kettlehole about 10 feet deep. Here is well illustrated one of 

 the ways in which reticulated kame ridges inclosing basins and depressions 

 are deposited by glacial streams as they shoot swiftly out of their narrow 

 channels or tunnels into a broader channel or into a lake or the sea. 



Not far south of the Mattawamkeag the osar begins again and con- 

 tinues somewhat interruptedly through Webster to the Mattagordus Stream, 

 in Prentiss. It then follows the valley of this stream for several miles south- 

 ward, expanding into a series of reticulated ridges inclosing kettleholes 

 The gravel here is very coarse, and cobbles, bowlderets, and bowlders 

 abound. Near the northwest corner of Springfield the system turns south- 

 west. It crosses the road from Springfield to Lee about midway between 

 those villages, consisting at that point of a low plain of well-rounded gravel 

 which incloses a small lake, the source of one branch of Mattakeunk Stream. 

 Just north of the road is a broad dome or hummock of morainal aspect, 

 since it is strewn with many bowlders 2 to 4 feet in diameter. Examina- 

 tion of these bowlders on faces not weathered shows that they have been 

 polished by water. These bowlders are granitic, like the far-traveled 

 bowlders of the surrounding district, while the osar-plain near it is com- 

 posed largely of slate and schists, like the local rock. The lower parts of 

 the till of that region are mostly derived from local schists and calcareous 

 and argillaceous slates. In the region east and northeast of Mount Chase 

 and Patten numerous granite outcrops have contributed a great number of 

 granite bowlders, and they are found covering the slaty till for many miles 

 to the south. The granite bowlders in Springfield and Lee are unusually 

 numerous, and there may possibly be an outcrop of granite somewhere to 

 the south of the Mattawamkeag, but careful inquiry has failed to find it. 



The situation may be summed up as follows: The osar-plain at this 

 point is composed chiefly of the same material as the lower part of the till, 

 while the outlying hummock resembles in composition the upper till. The 

 osar-plain shows few or no bowlders, while the hummock is largely com- 

 posed of them. The base of the outlying ridge is but little higher than 

 the osar-plain. Evidently the conditions under which these deposits were 

 formed were different in the two cases. There are numerous swells and 

 ridges of till near tliis place. During the final melting of the glacier the 



