Mineralogy and Geology of the White Mountains. 111 
No. 7 was not visited for want of time; but as I am informed, 
is similar to those last described. 
Porphyritic Granite. 
Proceeding E. from Plymouth, two and a half miles, we find 
boulders of this rock; soon the underlying rock, a decomposing 
pytitous mica slate crops out, and at three miles, porphyritic gran- 
ite appears in situ, and continues several miles, and along the 
north shore of Little Squam lake. This rock seems to con- 
sist of crystals of white feldspar, some of which are three to four 
inches long and two inches wide, and held together by quartz and 
mica, in about the same proportion to the feldspar as the cement 
of a breccia to the fragments. 
Common granite is found in situ at the top of the hill, after 
crossing the outlet of the lake ; but the boulders of the porphy- 
ritic granite are seen ~ Semitielot 1 in number, quite to Centre 
Harbor ; distant ten a from where they were first observed. 
Trap Dikes on Red Hill. 
Red hill or mountain, near Centre Harbor, Lake Winnipise- 
ogee, is usually ascended by visitors to enjoy the beautiful scenery 
of the numerous lakes, with their hundreds of islands, and also 
of several mountain ranges not very far distant from this peak. 
The mountain consists of reddish sienitic granite, and its sides 
are covered with fragments partly decomposed. Near the path 
leading to the top of the mountain are two dikes. 
No. 1 isa few rods north of the second house; seven feet wide ; 
course E. by N.; dip 15° to 20° N.; granite altered at junction, 
appearing baied and baked ; on the lower side the dike is expo- 
sed by the removal of the erandlio, and appears as an inclined wall 
afew feet high. The color and weight of the trap led some time 
ago to the supposition, that it was an iron ore, and several tons 
were quarried under this impression, which, upon better informa- 
tion, were never removed. 
Ns. 2 is one eighth to one quarter of a mile E. of No. 1. Course 
N. by E.; average width twenty-five feet ; dark brown ; slight 
lustre, owing to brown mica diffused wiGagh the mass; pyritous, 
and fires with steel. Near this, but separated eighteen inches 
from the dike, is a mass of trap several feet in dimensions, and 
pasted into granite. 
