KATAHUm SYSTEM. 107 



passes a short distaiace east of South Lincohi, and soon takes the form of a 

 single two-sided ridge, which takes a southeastward course and crosses the 

 Maine Central Railroad a short distance north of Enfield station (PI. V, 5). 

 North of Lincoln the osar is chiefly composed of small fragments of slate, 

 but in Enfield it passes through a granitic area and contains many 

 bowlderets and bowlders of granite, up to 2 i feet in diameter. I formerly 

 regarded the numerous bowlders on the surface as having been dropped by 

 ice floes. The proof is abundant that ice floes often did this, but recent 

 excavations in the osar in the northern part of Enfield show that water- 

 polished bowlders are scattered through the gravel to the depth of at least 8 

 feet. The latter are, therefore, a true part of the osar, though there are 

 some bowlders on the surface that are not water-polished on what seem to 

 be unweathered faces, and these may be floe bowlders. The ridge here is 

 30 to 50 feet high and of arched cross section. The osar passes a short 

 distance east of Enfield station and then traverses a great clay-covered 

 plain in the towns of Passadumkeag, Greenbush, and Greenfield. Much of 

 this plain is as level as the prairies of the West, and formed part of the 

 expanded Penobscot Bay. The flanks of the osar are here covered, often 

 deeply, with clays containing clams and other marine fossils. Both the 

 clay and the osar are sprinkled with occasional bowlders having the shapes 

 of till bowlders. There is nothing like a sheet of till overlying the clay, 

 and the bowlders indicate the work of ice floes rather than a readvance of 

 the glacier after the deposition of the clay. It is noticeable that more 

 bowlders were stranded on the hillsides than on the lowlands, and they are 

 most numerous on the north sides of hills, where the ice floes drifted as they 

 made their way down the bay. The Penobscot Bay at the time the sea 

 stood at 230 feet was 15 or more miles wide from east to west at this point. 

 In one place near the north line of Greenbush so many bowlders were piled 

 on the top of the osar that no attempt has been made to plow the surface. 

 A road is made on the top of the osar for many miles, the ridge forming a 

 natural roadway through the level and sometimes swampy region. The 

 osar here seldom rises more than 20 or 30 feet above the plain of marine 

 clay, but in three places in Greenbush it expands into a series of broad and 

 plain-like ridges, inclosing some kettleholes. The ridges here rise above 

 the level plain to a height of 100 feet. Rising so abruptly out of the plain. 



