472 ©. H. HMitchcock—Helderberg Rocks in New Hampshire. 
Logan. That can be found in the Huronian area flanking the 
Green Mountain range in Vermont, and possibly in the forest 
country about Connecticut Lake. The Swift Water series is 
more nearly related to the Helderberg. 
1. Porphyritic gneiss or granite.—This occurs at the corners 
of the towns of Littleton, Whitefield, Bethlehem and Dalton, 
forming an oval-shaped isolated area of about four square miles 
in extent. The Ammonoosuc River flows along its eastern 
border, and there is a large hill in the western or central part, 
about 600 feet above the river. This area is the most northern 
exposure of the porphyritic gneiss in the State. It is supposed 
to be connected with the great Lafayette-Moosilauk range be- 
neath the overlying Bethlehem group, and to be the oldest for- 
mation in New Hampshire. If compared with ancient systems 
of gneissic rocks elsewhere, it would agree best with certain 
portions of the Laurentian in New York and Canada. : 
2. Bethlehem gneiss.—As signified by the name, this formation 
is best develo in Bethlehem. It lies in a nearly east and 
west direction, disturbing the continuity of the newer systems, 
which usually trend northeasterly in its neighborhood. The 
disturbances may be seen in tracing the Cods and Helderberg 
groups from Lisbon into Littleton. The prevailing rock 1s 
very granitic in aspect, and often carries a hydro-mica in place 
of the common mica of gneiss. The feldspar is usually of a 
reddish cast. Two or three other areas of the same age occur 
in the valley of Connecticut River, in Haverhill, Lyme, Orford, 
Hanover and Lebanon. 
3. Gneiss.—This designation applies to a rock somewhat 
allied to No. 2, bounded by No. 1 on the north, and separated 
from the Cods group by No. 2. The valley of Littleton village 
seems to have been excavated mainly out of this area, and the 
absence of ledges in the lower ground makes it difficult to un- 
derstand its precise limits. The rock bordering No. 2 may be- 
long to this group, it being a mica schist slightly feldspathic, 
and abundant in the more southern areas of the Bethlehem for- 
mation. Mann's and Oak Hills in Littleton are the best expo- 
sures of this gneiss. It seems also to be distinct from the 
“White Mountain series” of my reports. 
4. Li Group.—The best part of Littleton, much of Mun- 
roe, and portions of Lisbon and Lyman are underlaid by 4 
series of greenish rocks consisting of conglomerate, hydro-mica 
and cupriferous schists, quartzites and dolomites, estimated at 
_ 4295 feet in thickness. A section roughly measured across the 
members, in the south part of Lisbon (see fig. 10), gave the fol- 
lowing order and thickness: first, hydro-micaceous conglomer- 
ates, 756 feet; second, hydro-mica schists with eupriferous layers, 
feet. The upper division often carries a nodular mass © 
