. 
G. W. Hawes—Eruptive Rocks in New Hampshire. 149 
and is composed of a very fine almost homogeneous ground- 
mass, in which small black shining erystals are porphyritically 
developed. The thin sections indicate that this is diorite. It 
is a mixture of hornblende, a triclinic feldspar, and titanic iron 
oxide. The large crystals are of hornblende; it is here an 
original product, and has not resulted from the alteration of 
pyroxene, as in the last case, since its well-formed crystals are 
developed in the common hornblendic forms. Many of them 
spar is a variety low in silica, but its species can not be deter- 
mined by optical means. The iron oxide is quite abundant, 
and in part well crystallized. Sometimes a large opaque 
ike No. 4 is about a hundred feet from No. 3 but is iden- 
tical with it in all respects. Di o. 3 separates into two 
branches in the middle of the stream, and forms two dikes in 
an island there situated, and it is not improbable that No. 4 
may unite with it at some point. : 
Dike No. 5 is about seventy-five feet from No. 4. It is very 
narrow, being only about a foot wide, but it has several 
branches as wide as itself which unite with it at acute angles. 
This again like No. 2 is composed of a fine grained ground- 
mass in which larger crystals are developed, but when the sec- 
tions are examined it is found to be an olivine diabase. The 
porphyritic crystals are in part perfectly formed augite crystals, 
and in part well formed olivine crystals which are mostly 
changed to serpentine. The finer portion of the rock is com- 
