74 GLACIAL (lEAVELS OF MAINE. 



those flowing south and east, at an elevation of about 900 feet. In the 

 eastern part of T. 9, R. 4, Aroostook County, a two-sided ridge extends 

 for about 3 miles along the east side of the Alegwanus or Blackwater 

 River, a stream which flows northwesterly into the Aroostook. The ridge 

 has rather steep lateral slopes, and is from 10 to 30 feet high. On the sur- 

 face it appears to be composed of till, but on digging down 2 or 3 feet, 

 true water-washed gravel is revealed. The pebbles are only slightly 

 rounded, yet the finest debris has been plainly removed by gentle currents, 

 and therefore the deposit is seen to be, not unmodified till, but the residue 

 after the action of water has removed the finest portion of the till and has 

 rounded and polished the larger fragments a very little. The ridge is here 

 composed of fragments of sedimentary rocks, which readily weather near 

 the surface of the ground, so as to lose their waterworn surfaces and to 

 resemble closely the stones of the upper layers of till. After an apparent 

 gap in the system of more than a mile, another ridge is found, extending 

 eastward, which is said to reach the northwest corner of Littleton, where 

 the sj^stem takes a more southerly course to Carys Mills, a short distance 

 west of Houlton Village. In this part of its course it several times crosses 

 low divides, and thus passes from one valley into another; and there are 

 several gaps in the system. 



Prof C. H. Hitchcock writes concerning this osar as follows:^ "A 

 short distance west of Houlton the same horseback reappears, being in 

 one place 90 feet high. The material of the ridge is sand, gravel, and 

 bowlders, indistinctly stratified. The sand of this horseback is black, and 

 there is no similar sand anywhere else in the county south of Houlton." 



On the same page is given a figure showing the internal structure of 

 the "horsebacks." Occasionally I have observed sections such as that given 

 in Professor Hitchcock's figure, but usually the osars have a more arched 

 stratification in the cross section. Not far north of Carys Mills the osar 

 extends into a broad ridge or plain, with some reticulated ridges as outlets. 

 This great abundance of gravel is found at the southern end of a long slope, 

 which, for 25 miles, has an average fall of about 20 feet per mile. The 

 pebbles and cobbles are very well rounded at this point, and a much larger 

 proportion of them are granitic than at the northern end of the system. 

 From Carys Mills the osar continues as a large ridge for several miles, 



'Preliminary report upon the natural history and geology of the State of Maine, p. 273, 1861. 



