37 
the tunnel is indicated, the presence of the column of 
limestone which appears to be within the main body of 
essexite of Mount Royal is due to an embayment in the 
periphery of the latter. 
THE ESSEXITE. 
The essexite exposed near the Lookout may be taken 
as representing the main body of the essexite intrusion of 
Mount Royal. It is coarse in grain, but varies somewhat 
in texture from place to place. It is composed essentially 
of pyroxene and hornblende with plagioclase and a little 
nepheline. The other minerals, which are present as 
accessory constituents, are olivine, biotite, sodalite (or 
nosean), orthoclase, apatite, iron ores, pyrite, sphene and 
zircon. 
The plagioclase and nepheline are always distinctly 
subordinate in amount, the rock consisting predominantly 
of augite and hornblende. In certain parts of the mountain, 
olivine becomes relatively much more abundant and the 
rock passes into an clivine-essexite (see page 38). 
The olivine, augite and hornblende have a marked 
tendency to assume idiomorphic development, some 
varieties of the essexite consisting of well defined crystals 
of these minerals embedded in a ground mass consisting 
chiefly of small laths of plagioclase. The augite and 
hornblende in a certain rare varieties of the rock are devel- 
oped as long narrow rod-like individuals, lying in parallel 
position and thus giving to the rock a peculiar and striking 
appearance. 
Pyroxene is the most abundant constituent in most 
varieties of the rock. It is of a purplish colour and fre- 
quently holds many minute black inclusions. Twinning 
is common and the individuals occasionally display an 
hour-glass structure. 
Hornblende usually ranks next in abundance. It is 
deep brown in colour, strongly pleochroic, and frequently 
occurs intergrown with the pyroxene or as a border about 
it. The hornblende separated from the coarse-grained 
essexite occurring in the Protestant cemetery was analysed 
by Prof. B. J. Harrington, with the results set forth in 
column III, page 39. As will be seen, it belongs to the 
class of basaltic hornblendes and is similar in composition 
to the hornblende occurring in the essexite of Mount 
Johnson. 
