158 Prof. O. P. Hubbard on Erosion in New Hampshire. 
Arr. XVIII.— The condition of Trap ected in ee ea pie 
an evidence and measure of Erosion; by Ouiver P. Huspa 
M.D., Prof. Chem., Min. and Geol., in Derunsouth Gollegeds 
In New pe ote geology is characterized chiefly by 
primary rocks and metamorphic slates—trap dikes are exceed- 
ingly numerous, and ree have an evident relation both in posi- 
tion and character to those of the adjoining states. Among them 
as to indicate a center of elevation, or greater resistance to ero- 
sion, than in the adjacent rock. This is the most northern of the 
peaks of Ossipee Mouutain, east of Leki Winnipisiogee ; it is de- 
scribed as “an isolated, bare, precipitous range of bluish green- 
stone rock,” and abundant fragments are found on the adjoining 
peak, covering the gneiss. From this . as a center, series of 
Hill, near Squam ale eu one inch to aaa feet wide, ranging 
east and west. ‘These dikes are distinctly marked over the 
surface of she granite including them. They have been worn and 
polished by the action of diluvial currents, so that a level and 
smooth surface, ng ace many thousand square feet, lies en- 
tirely bare of so 
In volume xxxiv. of this Journal, (p. 105,) I have described a 
number of trap dikes, presenting the same relations to the en- 
closing rock, and withont doubt there are hundreds of instances 
of the kind in New Hampshire and Vermont; and they are found 
at all levels, and continuons for considerable distances. The 
present condition of these dikes is, obviously, evidence of more 
or less erosion. I propose to cite in this paper, examples of trap 
dikes in New Hampshire and vicinity, which shall show how fat 
they are evidences and measures of erosion, whether ancient or 
recent 
The trap in New Hampshire occurs in relation to the surround- 
ing rocks either—1. Worn off smooth and plane with the adja- 
cent rock, whether the surface be horizontal or inclined—2. Be- 
low the surface, when in a state of decomposition and forming, it. 
may be, the channel of a stream—3. Prominent above, as at the 
Peak of Ossipee, and when forming an occasional barrier of a 
stream, where the surrounding rock has been remove 
There are believed to be very few instances of the third con- 
dition. Bear Camp river is crossed by a dike one to two feet 
* Geology of New Hampshire, p. 72. 
