- 
Prof. O. P. Hubbard on Erosion in New Hampshire. 159 
wide which forms a barrier, the granite having decayed away. 
There may possibly be an instance in Red Hill, where the dike 
is exposed on one (the lower?) side by the removal of the 
ite.* ; 
(a.) Of the second kind, there is an example in the rear of ¢ the 
Willey house, referred to by Mr. Lyell in his second tour, and de- 
scribed by me previously in volume xxxiv. of this Journal. The 
trap is the bed of a small mountain torrent, in some parts decom- 
posing, in others very hard. This dike was traced this season by 
some members of our party,{ along a continuous and deep channel 
far up the mountain, and it is there found to divide into two parts, 
which again meet a considerable distance above, and thus enclose 
a large elliptical area. This area is distinctly observable from the 
direction of the channel is north 80° east. At its lower end on 
the right hand is a trap dike, in several distinct lines each a few 
inches wide, mounting high in curved plates in the side of the 
cliff ; farther on they decline and coalesce into one dike twenty 
inches wide, which passes under the water. 
_ The dike crosses the fissure obliquely at about N. 75° E., and 
1S Seen some rods farther up the stream in a vertical section ex- 
tending to the top of the opposite bank. 2 
"he trap where constantly wet is softened and decomposing, 
and above on the sides, is compact, very much fissured and stained 
deep with oxyd of iron. ‘This fissure, like the former, must be 
admitted to have been filled by the intrusion of trap, and to have 
ome a water channel by the removal of the dike; the chan- 
“hel, therefore, is some measure of the erosion of the trap and its 
rocky enclosures by existing agency. 
¢ description given in the Geology of New Hampshire 
of the beautiful Dixville Notch, in the northern part of the state, 
Suggests sitnilar conclusions. 
ans eR 
* Am. Jour. Sei, vol. XXxiv, p: 113. + Thid, p. 1It. 
+ Members of the Senior Class in Dartmouth College. 
