Prof. O. P. Hubbard on Erosion in New Hampshire. 167 
_ (g.) Moose Mountain is a part of a north and south range of 
mica and hornblende slates with quartzite. It is situated about 
eight miles east of Dartmouth College, and may be 1000 feet 
high. Between the granite knobs just east of the College and 
the range, there is a synclinal valley and axis, and the slates on 
Moose Mountain dip westerly at a high angle. In passing along 
the ridge some years since, I observed a depression eighteen feet 
wide with perpendicular sides twelve feet high, and this singular 
interruption of the line of the ridge led to an examination of the 
rock in this space. It proved to bea dike of columnar porphyritic 
trap running east and west, which was traceable some way down 
the declivity, but of a uniform surface with the sides of the 
mountain. ; 
On the opposite side of the valley, and crossing it and the road 
obliquely and following exactly the undulating and channeled 
surface of the slate, is another very compact, hard, blue trap dike, 
with crystals of glassy feldspar, and fourteen feet wide. These 
dikes if produced must intersect each other, and the latter is cut 
own many feet by a small stream. 
A few miles south where this ridge is interrupted by the valley 
of the Mascomey River or Enfield Pond, the precipitous bluff 
presents a dike some feet in width which is made up of flattened 
and rounded masses of trap in columns side by side, and rapidly 
decomposing. ‘This is one hundred feet and more above the 
level of the lake, which is at the base of the ridge, and whose 
bed must be intersected by the dike. 
(h.) Mount Washington, as I showed in the American Journal, 
XXXiv, in 1838, is covered or capped with mica slate i place— 
and as there is no evidence from diluvial scratches, boulders or 
rounded and smooth surfaces, of erosion or denuding forces, we 
infer that its peak ever has been above the reach of those agen- 
cies which have operated upon its flanks and upon the surround- 
Ing peaks. 
If a fissure should occur through one of these granitic peaks 
from valley to valley, (it would probably be much farther ex- 
tended, ) and if molten lava were to fill this fissure, it could never 
teach the apex or remain consolidated there, unless it were sup- 
ported at the dimits of the fissure on the flanks of the mountain. 
It is contrary to physical laws that as the lava rose in the fissure, 
it should not gravitate and run into the lower places, the valleys 
on the sides of the mountain, and only as these were filled would 
it rise in the fissure, and equally in both. This must follow 
whether the surface be submarine or subaerial. 
1. If the existing valleys were filled to the height of the peak 
With diluvium or drift, like the conglomerate hardpan of this re- 
8ion, which is so consolidated that when excavated it must be 
sted, this would seem sufficient to repress or hold up the col- 
