MODIFIED DRIFT ALONG MERRIMACK RIVER. 79 
below this normal line, which is here shown on the west side in the plains 
north and south of Fisherville. 
Boscawen village is built on the south end of a similarly sloping terrace 
three miles long, in which distance it falls 30 feet, and we find 30 feet 
more fall of the same terrace in less than a mile along the village street. 
The whole of this terrace is below the normal height, showing a defi- 
ciency of 15 feet at its beginning, and of 40 feet at the north end of Bos- 
cawen village. It appears as if the supply of alluvium was insufficient, 
and the direction of the current at first caused it = 
to be deposited in greatest amount at one side, 
without filling the valley. South of Boscawen the 
«‘Whale’s Back’’ 
Kame, 350. 
350. 
supply of material became still more inadequate, City of Concord. 
290. 
and the lower portion of the sloping plains east 
of the river was probably 60 feet below the surface 
of water, which was held back by the extensive 
plains of Concord, derived in large part from the 
Contoocook and Soucook valleys. 
R. R. 252. 
240. 
R. 227. 
240. 
weeer rede resee 
me Ae 
Although the plains in Concord were obviously 
¥ 
brought in from tributary sources, they belong to 
the ancient flood-plains of the Merrimack, since 
*GYOONOD NI NOILOTS—"61 “31 
they form a portion of the series of high terraces 
and plains which extends with a slightly varying 
but unbroken slope along this whole valley. Even 
if no modified drift were supplied, except from the 
upper part of the main valley, irregularities of 
slope, as in Boscawen and Canterbury, with in- 
creased height below, as in Concord, would still 
be produced by an irregular rate of retreat of the 
ice-sheet, allowing long and abundant deposition 
in some portions, but much less in other portions 
of the same valley. In this way we must explain 
the sudden and permanent increase in height of 
the upper terrace of Connecticut river at North Thetford (p. 36). Prob- 
ably this cause was combined with the aid of tributaries to produce the 
high plains in Concord and southward. 
Between Fisherville and West Concord these plains have a large 
an pers enenenane 
‘OSE ,,‘sureyd eC, 
*soqttu ¥€ ‘yysuaT 
“SOULS 
a Soucook river, 
“vas DAO(EMera awa weenvesss 
