: ‘may be indicat 
570 C. H. Hitchcock—Helderberg Rocks in New Hampshire. 
stone. ‘For twenty rods beyond, the rock is purely hornblende, 
and is 300 feet thick. The strata are concealed for 180 rods 
along the line of section, which must be 2,400 feet thick, if 
their inclination agrees with those upon both sides. Just be 
yond is a black slate, exposed at a railroad crossing at the 
north end of Lisbon village, which is the last member of the 
series, and has been traced along the strike for eight miles, 
from near a saw-mill on Wetherbee’s Mill Brook in Lisbon to 
the line of Haverhill. The total thickness of the Swift Water 
series on this section seems to be over 4,400 feet. 
ttention was directed to this group partly by the slate 
bands and partly by a nondescript conglomerate adjoining it, 
particularly noticeable a mile and a half north from Lisbon, 
west of Mr. A. Bishop’s, on the northwest side of the river. 
The pebbles are not discernible till the rock has been weathered 
nearly white, and even then it is difficult to understand their 
character. This band is not more than fifty feet thick. 
Following up the wild Ammonoosuc River in Bath, there is 
a characteristic representation of this series of strata, and our 
name is derived from that of a small village on its banks. 
The facts given are chiefly from the notes of J. H. Huntington. 
The Lisbon group seems to extend up this stream for more 
than a mile above its mouth, judging from its general distribu- 
tion. A little above a starch-factory, fig. 11, there are strata 
of micaceous conglomerate of gneissoid aspect, dipping 40° N. 
58° W. The slate, or the continuation of the Lisbon band, is half 
a mile above the factory, and dips 65°, N. 70° W. Less than 
half a mile above is a more distinctly gneissic band, dipping 
56°, N. 50° W. About the village of Swift Water are various 
exposures of a whitish mica schist, from 40° to 55° dip in the 
same general direction. There seems in many cases to be 
feldspar present; certainly a hasty look would make the ledges 
glossy black micaceous bands of a few inches in thickness 
interstratified with the quartzites. This is at a bridge one an 
a half miles above the village. A wide band of hornblende 
schist below the bridge should not be forgotten. The gneiss 
above has a high dip. It is possible that an anticlinal axis 
ek by the divergence in the steepness cf the dips. 
_ there seems to be a prolongation of a spur from the gneiss ~ 
_ Haverhill directly to the point of dip-divergence. There is 
