Wright.] 48 pecember 20, 



quently by tourists and geologists. In the i( Transactions of the 

 Association of American Geologists and Naturalists," for 1841 and 

 1842, Pres. Edward Hitchcock, of Amherst College, gave a de- 

 tailed account of the formation so far as then observed. 1 He there 

 characterizes it as " decidedly the most interesting and instructive 

 case [of the kind] which he had met with." A map of a mile and 

 a half of it, then supposed to be its limit, was given by Prof. Hitch- 

 cock in the same paper, prepared by Prof. Alonzo Gray. This 

 map, on a reduced scale, reappears in " Hitchcock's Elementary 

 Geology." 2 Some other ridges of a similar nature were noticed by 

 that eminent observer, and the suggestion was made by him that far- 

 ther researches might show a system where now only a confused 

 group was observed. 



We could not improve upon the description of the main features of 

 this formation given by Dr. Hitchcock, in 1842. 



" Our moraines form ridges and hills of almost every possible 

 shape. It is not common to find straight ridges for a considerable 

 distance. But the most common and most remarkable aspect 

 assumed by these elevations is that of a collection of tortuous ridges, 

 and rounded, and even conical, hills with corresponding depressions 

 between them. These depressions are not valleys, which might have 

 been produced by running water, but mere holes, not unfrequently 

 occupied by a pond." 3 



By reference to Plate 1 , and the description here given in connec- 

 tion with it, the characteristics of this formation may easily be ap- 

 prehended. 



At Smith and Dove's Flax Mill, near Andover Depot, a dam 

 raises the Shawshin River 14 feet. Measuring 4 from the river bed 

 below the dam, the ascent to the peat bog, o, at the base of the east 

 ridge is, in round numbers, 41 feet. Taking this bog as a level, the 

 height of the successive ridges, East Ridge, Indian, and West, at 

 the points a, b, and c, is 41 feet, 49 feet, and 71 feet. The point c, 

 however, is in a characteristic depression of the ridge. On either 

 side of it, north and south, prominences project 20 feet higher, 



1 See page 198. 



2 See page 260 (30th edition). 



3 Transactions of American Association of Geologists and Naturalists for 1841 

 and 1842, p. 191. 



4 The measurements were made under my superintendence by the class of 1875, 

 Phillips Academy. 



