84. SURFACE GEOLOGY. 
Between West Concord and the city the upper terrace is from 10 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 367 feet above the sea, being higher than 
the plains of the east side. 
Kames in Merrimack 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 
