69 
above mentioned, a considerable amount of oligoclase is 
really present. The feldspar individuals, both great and 
small, usually show in thin sections the mottled character 
due to the intergrowth of different species described in 
the pulaskite. A partial analysis of a specimen of this 
intermediate rock, from the south side of the mountain, 
is given in the table of analyses on page 73 (No. VI). 
As will be seen it is intermediate in chemical composition 
between the essexite and the pulaskite, occurring on either 
side of it, thus representing an intermediate zone in which 
the differentiation was not quite completed. It is, how- 
ever, much more nearly allied to the essexite. 
Essexite.—The rock is: dark in colour and rather 
coarse in grain, and while holocrystalline, usually presents 
a more or less marked fluidal arrangement of the con- 
tituents. This is especially marked in the zone of tran- 
sition between the essexite and the pulaskite, owing to 
the presence there of the large feldspar phenocrysts which, 
being arranged with their longer axes parallel to the direc- 
tion of flow, serve to accentuate this structure. The finer 
grained variety forming the summit of the mountain is 
more massive in character and does not exhibit the fluidal 
arrangement of constituents. Under the microcsope the 
rock is seen to be composed of the following minerals: 
hornblende, pyroxene, biotite, olivine, plagioclase, nepheline, 
sodalite, apatite, magnetite, sphene, and in some cases 
a very small amount of orthoclase. 
There is a marked tendency on the part of all the 
constituents to assume an idiomorphic development. The 
long lath-shaped plagioclases and large hornblende indi- 
viduals have an approximately parallel arrangement, and 
between these lie the other iron-magnesia constituents 
with the smaller plagioclase individuals, the nepheline and 
the other components of the rock. These interstitial cons- 
tituents do not differ greatly in size from the others, and 
show the same tendency to a parrallel arrangement. 
Hornblende is present in almost every thin section 
of the rock along with pyroxene and biotite, but the 
relative proportion of these minerals varies considerably. 
The hornblende is distinctly the most abundant, except 
in the finer-grained variety forming the summit of the 
mountain, in which it is distinctly subordinate in amount 
to both pyroxene and mica. It is deep brown in colour 
and is sometimes hypidiomorphic in its development, but 
