Prof. O. P. Hubbard on Erosion in New Hampshire. 161 
river enters a rocky channel, called “The Gulf,” at a large angle 
with its previous course, and runs S.S.W. with a rapid descent for 
nearly a mile. The left bank (in the descent) is nearly vertical, 
though receding at top, and by estimate one hundred feet high, 
and the opposite bank, with various irregularities, is in part and 
in some places entirely made up of a trap dike from three to six 
and ten feet thick, whose course is N.N.E. and dip 58° south- 
easterly, and coincident in these respects with the mica slate en- 
closing and underlying it and parallel of course to the stream. 
It has here and there been crossed by the stream and extensively 
removed with the slate below it, and a channel has been made 
on both sides which is filled at high water; and again the dike is 
found enclosing the slate and is extremely hard and compact. 
Passing off at right angles to this dike, as lateral branches, and 
crossing under the stream, are two other large vertical dikes which 
Srconp Serizs, Vol. IX, No, 26.—Feb.,, 1850. 21 
