1877. ] Surface Geology of the Merrimack Valley. 533 
A portion of the Andover series of kames was described by 
Dr. Edward Hitcheock,! in 1842, which appears to be the earliest 
notice of these peculiar gravel ridges in America. He writes: 
“The most common and most remarkable aspect assiimed by 
these elevations is that of a tortuous collection of 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 un- 
frequently occupied by a pond.” 
The extent of this series was at first supposed to be about one 
and a half miles, but Rev. George F. Wright? has recently 
traced it fully twenty-five miles, from Methuen to Wakefield. 
He has also traced a second parallel series, which lies about 
seven miles farther east, passing through Haverhill, Groveland, 
Georgetown, Boxford, Topsfield, and Wenham. These ridges 
“are ordinarily composed of sand, gravel, and pebbles, the latter 
from a few inches to two or three feet through, sometimes irreg- 
ularly stratified, the coarse material being as likely to abound 
near the top as at the bottom; at other times ten or fifteen feet 
or more in thickness will give no sign of stratification whatever. 
- ++. The fragments of rock in the ridges are nearly all some- 
what rounded and apparently water-worn.” The first of these 
Series is well shown in Lawrence, a short distance southeast from 
the water-works reservoir. On the west side of Shawshin River, 
Opposite Andover village, it consists of three parallel kames» 
own as East, Indian, and West ridges, which are respectively 
forty, fifty, and ninety feet high. The last two inclose a bog 
filled with peat and mud, twenty to thirty feet deep. The base 
from which these measurements were taken was forty feet above 
Shawshin River and ninety feet above the sea. 
Prominent hills, composed of unmodified drift or till, are scat- 
tered here and there along the course of the Merrimack River 
through Massachusetts, and in some townships are almost as 
thickly set as possible. These remarkable accumulations of till 
are readily recognized because of their smooth and regular con- 
tour. From their resemblance in shape to a lens, Prof. C. H. 
Hitchcock has denominated them lenticular hills. They are ob- 
ong or sometimes nearly round, with steep sides and smoothly 
rounded tops, and vary from an eighth of a mile to a half mile in 
length, and from forty feet to two hundred feet in height. ‘Their 
1 Transactions of the Association of American Geologists and Naturalists. 
s ings of the Boston Society of Natural History, vol. xix., pp. 47-63. 
