70 SURFACE GEOLOGY. 



and east. Nearer to the river here we have a lower terrace only from 5 

 to 10 feet above it. In the excavation of the gravel deposits, the river 

 has sometimes left numerous and well marked terraces, though small in 

 extent, and differing but little in height. This is well shown near Tut- 

 tle's, in Lincoln, where four distinct terraces are seen between the road 

 and the river, with from 3 to 5 feet escarpments, the highest being about 

 20 feet above the river. 



The height of terraces in this valley was determined by levelling only 

 as far north as to the mouths of East Branch and Moosilauke brook, 

 which enter the Pemigewasset, from opposite sides, at nearly the same 

 point. The river here is 710 feet above the sea, or only 242 feet higher 

 than at Plymouth, eighteen miles farther south. Profile lake, its source, 

 nine miles to the north, is about 1,950 feet above the sea, by barometric 

 measurement, showing a descent to this point of more than 1,200 feet.* 



The plains above the East Branch, not determined by the level, appear 



to be somewhat lower than the highest modified drift just south of this 



stream. This terrace has a height of 70 feet above the sea, and is ten 



feet higher on the west side. Thence for ten miles southward, or nearly 



to the south line of Thornton, the highest terrace of the river, commonly 



well shown on both sides, has a uniform continuous slope of 15 feet to 



the mile. This is nearly the same as the descent of the river, which 



has cut its way from 70 to 100 feet deep through its former wide, sloping 



flood-plain. These remnants, lying at corresponding heights on opposite 



sides of the river, and sloping with it in the regular lines of the upper 



terrace, are here very interesting, as seen extending for miles up and 



down the valley. Nowhere else in New Hampshire is the erosion of 



o the modified drift, by which it 



pi ^ ^ has been shaped in terraces, so 



/ ^ "700 ft clearly and convincingly display- 



^. ^ „, 1 . ^ cd. Here no doubt can remam 



Fig. 17. — Section in Woodstock, ih miles 



BELOW THE MOUTH OF East BRANCH. that an Original flood-plain, ten 



Length, | mile. miles long, has been terraced as 



we see it by the excavation of the river. For most of the way along 



*The errors which occur in Vol. I, pp. 288, 308, and 322, in stating the height of Pemigewa.sset river at the 

 mouth of East Branch, and of other points in this vicinity, arose by computing barometic observations from 

 Thornton, which, through some mistake, is given 600 feet too high by Prof. Guyot, among the usually very cor- 

 rect altitudes published in his memoir on the "Appalachian Mountain System." 



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