. The geology of New Hampshire : a report comprising the results of explorations ordered by the legislature. and Soucook valleys. Although the plains in Concord were obviouslybrought in from tributary sources, they belong tothe ancient flood-plains of the Merrimack, sincethey form a portion of the series of high terracesand plains which extends with a slightly varyingbut unbroken slope along this whole valley. Evenif no modified drift were supplied, except from theupper part of the main valley, irregularities of ^ ^slope, as in Boscawen and Canterbury, with in-creased height below, as in Conco
. The geology of New Hampshire : a report comprising the results of explorations ordered by the legislature. and Soucook valleys. Although the plains in Concord were obviouslybrought in from tributary sources, they belong tothe ancient flood-plains of the Merrimack, sincethey form a portion of the series of high terracesand plains which extends with a slightly varyingbut unbroken slope along this whole valley. Evenif no modified drift were supplied, except from theupper part of the main valley, irregularities of ^ ^slope, as in Boscawen and Canterbury, with in-creased height below, as in Concord, would stillbe produced by an irregular rate of retreat of theice-sheet, allowing long and abundant depositionin some portions, but much less in other portionsof the same valley. In this way we must explain < gthe sudden and permanent increase in height of f^the upper terrace of Connecticut river at North Thetford (p. 36). Prob-ably this cause was combined with the aid of tributaries to produce thehigh plains in Concord and southward. Between Plsherville and West Concord these plains have a large. 80 SURFACE GEOLOGY. extent, lying on the south side of Contoocook river. Their northern andwestern portions are 125 feet above the Merrimack river at the head ofSewalls falls, but they become slightly lower at the south. The mouthof Contoocook river is 249 feet above the sea. Its descent through Fish-erville, in the last mile and a half of its course, exceeds 100 feet. By theBorough dam, at the head of these falls, this river is held level to Con-toocookville in Hopkinton, six miles in a direct line. Along this distanceand beyond we find extensive alluvial areas at small elevation above theriver, continuous with these plains in the Merrimack valley. A descrip-tion of the modified drift of Contoocook river will be hereafter presented. The most extensive plains in Concord, and indeed in this entire valley,lie on the east side of the Merrimack between it and the Soucook
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