84 SURFACE GEOLOGY. 



Between West Concord and the city the upper terrace is from lo to 30 

 feet lower than on the east side of the river. The greater part of the 

 city, and a large area southward to Turkey river, are slightly lower, being 

 about 300 feet above the sea, or 75 above the river. In the west part of 

 the city the modified drift, composed of sand or fine gravel, rises unter- 

 raced into irregularly sloping hills, the highest of which, crossed by 

 Church and School streets, are },6j feet above the sea, being higher than 

 the plains of the east side. 



Kamcs in JSIerrimack Valley. 



Interesting kames are found at Concord, where they form the uneven 

 east part of Blossom Hill cemetery, and extend south in a nearly continu- 

 ous series, composed of irregular, short, low ridges and mounds, always 

 with north to south trend, to the intersection of Franklin and High 

 streets, and thence on the same course to Centre street. The south por- 

 tion of this series is a single steep ridge, from 25 to 40 feet high, called 

 "Whale's Back," which originally extended a quarter of a mile from near 

 the corner of Centre and Pine streets to that of Warren and Liberty 

 streets. The north half of this has been used by the city in making and 

 repairing streets; for which this gravel, when screened to remove its 

 coarse pebbles, forms an excellent surface, and ultimately the whole ridge 

 will thus be removed. The material of "Whale's Back" is mainly very 

 coarse gravel, containing abundant pebbles up to one foot, while the larg- 

 est reach two or three feet in diameter. These are always well rounded, 

 having the characteristic water-worn form, — not that of glaciated boulders, 

 which are distinguished by flattened, striated sides, with rounded corners 

 and edges. This water-worn gravel lies in a steep, narrow ridge, a sec- 

 tion of which usually shows an indistinct anticlinal bedding. The round- 

 ed boulders, pebbles, and fine gravel are almost indiscriminately mingled 

 through the whole mass, often with very scanty streaks of sand or other 

 lines of stratification. 



This series of kames lies at the west margin of the wide alluvial area, 

 resting upon till 100 to 125 feet above the river. Its extent is a mile and 

 a half, having the same course with the valley. No kame-like deposits 

 were discovered along the east side of the river in Concord, the whole 

 mass of the plains being fine alluvium. Similar ridges were next found 



