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SURFACE GEOLOGY. 



shape. Of these the four longer sides are usually striated parallel to 

 each other. 



My attention was called to this as a typical shape by examination of 

 certain large striated boulders. In 1856, a boulder of red sandstone was 

 exhumed in Amherst, Mass., 6i feet long, 5^ broad, 2I thick, having 

 strise upon the four longer sides parallel to each other.* This was de- 

 scribed as something unusual. I found in Quebec, a few years later, 

 similarly striated boulders somewhat larger; and in the glacier de 

 Bossons in Chamouni, at the foot of Mt. Blanc, I noticed the same trape- 

 zoidal figures in a very large stone, 40 by 27 by 12 feet in its dimensions. 

 It was striated on the same four sides as the others, and had the ends 

 rough. It lay just below the ice, with its longer axis parallel to the 

 course of the glacier. Since that time I have always observed the shape 

 of glaciated stones, and think the majority have the same form with 

 these that I have mentioned. Originally rough, and possibly somewhat 

 rectangular, they have been both ground down and striated by the slid- 

 ing over them of the glacial rasp, or have been themselves fastened into 

 the foot of the ice, and ground over other stones and rocks. After miles 

 of scouring, the largest boulders might be worn symmetrically to the size 

 of pebbles. On scrutinizing the shapes of stones in the till, one can fre- 

 quently find various stages of this process preserved. In Derry and 



Salem I noticed a large number 

 of flat stones, of which only one 

 T-=^^^^^ side had been smoothed. Let the 

 i^/^^^- circumstances be changed so that 



these boulders be turned over, and 

 the present upper rough side will 

 be glaciated, and the whole be- 

 come symmetrical. A few have 

 several faces upon them, as if they had been fastened in the paste several 

 times. Fig. 58 shows a glaciated stone in Moultonborough, striated in 

 the usual way, and also by a second set (b) across the preceding. It is 

 30 inches long, 14 thick, composed of trap, and lies by the roadside upon 

 a mass of till. 



A more interesting case has been partially preserved in the Hanover 



Fig. 58. 



-Glaciated Stone, Moulton- 

 borough. 



• American yotirnal of Science, ii, vol. xxii, p. 397. 



