150 GLACIAL GRAVELS OF MAINE. 



is a two-sided ridge, or often a terrace on the hillside west of Half Moon 

 Stream and 50 feet or more above the stream. It skirts the eastern slopes 

 of a hig-li hill in Unity and Knox, and near Chandlers Comer crosses the 

 north branch of Half Moon Stream, and within one-eighth of a mile 

 disappears as a two-sided ridge. Here it required careful observation to 

 determine the course of the glacial river, and the result was quite unex- 

 pected. The ridge seems to be lost at the northern base of a range of hills 

 300 to 500 feet high. This range is several miles in length and has a 

 northeast-and-southwest direction. Along its northern base is a depression, 

 or valley, occupied by the south branch of Half Moon Stream, which flows 

 northeastward. It is from 100 to 400 feet wide and from 20 to 40 feet 

 deep. In places nothing but till can be seen in the steep banks inclos- 

 ing- it, and it looks like a large canal cut in a deep sheet of till. In other 

 places there is a steep wall or cliif of solid rock 10 to 30 feet high, gla- 

 ciated on the top, bordering the valley on the north, and it is thus proved 

 to be, in part at least, a valley of preglacial weathering and erosion. It is 

 parallel with the strike of the upturned pyi'itiferous and other easily weath- 

 ered slates and schists characteristic of this region. The depression, being 

 transverse to the direction of general glacial movement, became more or 

 less filled with till. The bottom of this valley is covered by a level-topped 

 plain of sand and well-rounded gravel 10 to 20 or more feet in thickness 

 and 1 to 400 feet wide. The south branch of the Half Moon Stream flows 

 in this valley for aboiit 2 miles, but it is a small brook, such as ordinarily 

 has in that region a flood plain containing only 1 to 3 feet of gravel, the 

 stones of which have the till shapes almost unchanged. Plainly it is incom- 

 petent to deposit any such plain of sand and rounded gravel as that found 

 in its valley. At one place the brook soaks into the gravel and disappears 

 except in time of flood, when it can not seep into the gravel as fast as the 

 flow from above, and the surplus water then for a time escapes by an over- 

 flow channel over a rough and crooked bed evidently recently eroded in 

 the till and gravel. As this channel is dry most of the time, it is locally 

 known as the "Dry Stream." The water which disappears in the gravel, 

 as above described, comes out again about one-fourth of a mile below in 

 the form of boiling springs, which are eroding the gravel more rapidly, 

 working from beneath, than both the main stream and the overflow stream 

 combined are eroding it above where the water disappears in the gravel. 

 In this way the gravel plain has been eroded for more than one-fourth of a 



