MODIFIED DRIFT ALONG MERRIMACK RIVER, 



75 



south of the East Branch. The same rapids continue a mile or two be- 

 low Bristol, so that the total descent in six miles from New Hampton 

 bridge to the mouth of Smith's river is ii8 feet, or from 438 to 320 feet 

 above the sea. The westerly course of the Pemigewasset here corre- 

 sponds to that of Connecticut river along Fifteen-miles falls. These are 

 the only considerable deviations of these rivers from their general direc- 

 tion in the state ; both portions are of rapid descent over till ; they are 

 alike bordered by sloping hills ; and both differ from all the rest of these 

 valleys in being well-nigh destitute of modified drift. Remnants of the 

 original high flood-plain, now forming the normal upper terrace, traceable 

 on both sides nearly all the way from the East Branch to Massachusetts 

 line, appear to occur in the highest of two terraces at the mouth of Ten- 

 mile brook ; in a small, gently sloping plain about midway between New 

 Hampton and Bristol; and in a similar area east of the highway a short 

 distance north of Bristol. All these are on the north side of the river, 

 and are from 510 to 500 feet above the sea. At several places along 

 these rapids it appears probable that the channel has been cut through a 

 considerable depth of till. 



Bristol village is built almost wholly on till or ledge. Below Main 

 Street bridge the fall in Newfound river is 105 feet, and its total fall from 

 Newfound lake is 238 feet, the lake being 590 feet above the sea. The 

 usual display of terraces again commences opposite Bristol, and thence 

 the alluvial area extends, with the river, unbroken through the state. 



At the mouth of Smith's river the highest terrace, 460 feet above the 

 sea, is wide for a mile to the north, and extends in a narrow strip for the 

 same distance to the south. Thence southward to Franklin we find re- 

 mains of the same, principally on the east side, from 480 to 440 feet above 

 the sea. In the south part of Sanbornton they form an extensive plain, 

 475 feet above the sea, probably slightly increased in height by the tribu- 

 tary alluvium of Salmon brook, which has cut a channel along its south- 

 east side. From this plain a wide terrace (from 475 to 440 feet) extends 

 south on the east side to Franklin, where the normal upper terrace is 

 again shown on both sides of the valley, forming on the west the high 

 sandy plain, 445 feet above the sea, which extends a mile north-west to 

 Webster lake. 



Lower terraces are numerous on both sides for a mile below Smith's 



