64 
which in its turn loses its porphyritic character and passes 
into a coarse-grained essexite which constitutes the mass 
of the hill, and which becomes at the summit finer in 
grain, richer in pyroxene and often holds a little olivine. 
No sharp lines can be drawn between these several rocks; 
one passes gradually into the other, the whole constituting 
one intrusive unit. The approximate limits of these 
several rock species are shown in the accompanying map 
and photograph of the mountain, it being impossible 
sharply to delimit the several species. The mass therefore 
becomes progressively more basic from the margin of the 
intrusion to its centre. The two chief rock types are the 
pulaskite and the essexite which will be separately consid- 
ered. 
The Pulaskite.—This soda-syenite which, as above 
mentioned, forms the outer zone of the intrusion, girdling 
the essexite, is less abundant than the latter, and differs: 
greatly from it in appearance. This difference is due 
chiefly to the fact that it is pale yellow or buff in colour, 
instead of dark grey, the lighter colour being due to the 
very small proportion of iron-magnesia constituents 
present and the marked preponderance of the feldspars. 
The rock also has a more massive structure without the 
fluidal arrangement of constituents often met with in the 
essexite, and it weathers in a somewhat different manner. 
It possesses, moreover, a species of porphyritic structure, 
owing to the development of the feldspar in two forms; 
first, as stout prisms, up to 10 mm in diameter, which are 
light grey in colour and very abundant; and, secondly, 
in the form of sma'ler laths of a yellow or buff colour 
which, in association with the iron-magnesia and other 
constituents, form a sort of ground mass in the rock. 
The constituent minerals of the rock are biotite, 
hornblende, soda orthoclase, nepheline, sodalite, apatite, 
magnetite and sphene. The darker contituents are 
identical in character with those occurring in the 
essexite. Not only are they as a class much _ less 
abundant in this pulaskite, but the mica here preponderates, 
while the hornblende is much less abundant and the 
pyroxene is entirely absent. It may be noted, however, 
that the hornblende sometimes possesses the greenish 
tint referred to as occasionally seen about the borders 
of the hornblende individuals in the essexite, indicating 
probably that the pulaskite magma being richer in soda, 
