234 



IRVING B. CROSBY 



rocks prevail in the northern part and granitic rocks in the southern 



part. The country is heavily mantled with glacial drift; but the 



existing bed-rock contours indicate that the preglacial topography 



- was in the mature stage of dissection. 



z ^ • 



^^.^„^o.5- -.*„,.o~ The river flows southerly through this 



province, in a broad valley, descend- 

 ing 1 80 feet in 30 miles, or 6 feet to 

 the mile. 



The middle province extends from 

 Berlin, New Hampshire, on the west ■ 

 side of the main ranges of the White 

 Mountains, to Bethel, Maine, on the _ 

 east side, its high mountains and deep ^ 

 valleys contrasting strongly with the 

 lower mountains and broad valleys 

 of the upper province. The Andros- 

 coggin flows southerly from Berlin to 

 Gorham through a narrow valley in 

 granitic rocks, and then turns abruptly 

 to the east and passes, in a deep valley, 

 through high mountains of massive 

 siliceous schists. These schists, the 

 most resistant rocks of the region, 

 form the main ranges of the White 

 Mountains, and extend northeasterly 

 into Maine. 



In the middle province the river 

 descends 420 feet in 30 miles or 14 

 feet to the mile, thus having a gradi- 

 ent two and one-third times as great 

 as in the upper province. At Berlin 

 the river drops 200 feet in several 

 falls; and there are a number of 

 other falls and rapids in the first ten 

 miles below that city. Profile i 

 (Fig. 2) shows the distribution of fall 



on the river and emphasizes the contrast of the river gradients 



above and below Berlin, 



Fig. 2. — Profiles of the present 

 and former courses of the Andros- 

 coggin Drainage 



