6 BULLETIN OF THE |. 
From what has now been said, it seems certain that a feldspar as basic 
as labradorite-exists in the rock. ‘This is attested both by the high ex- 
tinction angles in the zone of oP and « P&%, as well as by the presence 
of calcite as a significant product of alteration. That a feldspar less 
basic than oligoclase, and probably as acid, is present also, is shown by 
the zonal structure and wide range in specific gravity. The potassium 
obtained from No. 222 may be derived either from alteration products 
(muscovite?) or from the feldspar itself. The analysis of this rock 
in toto, which may be found in the sequel, shows by the small amount 
of hydration that little alteration has taken place. It therefore seems to 
be certain that the potassium is derived from the feldspar itself, either 
from orthoclase or from a potash plagioclase. 
The principal non-feldspathic constituent is augite, which is much 
broken up by feldspar crystals, though rarely the feldspar is penetrated 
by augite, showing the nearly contemporaneous formation of the two 
minerals. The augite, which has generally a rose color, displays a faint 
dichroism, the ray parallel to b being pink, and that parallel to q pink- 
ish yellow. Both prismatic cleavages are generally well developed, and 
intersect on the basal plane with the pyroxene angle 87°. Parting par- 
allel to © P% and occasional twins according to the same plane, though 
not constant features, are observed in the rock from some localities. 
Zonal structure is not uncommon, and rarely the hour-glass structure is 
well developed. The principal alteration is to uralite, which is found in 
rims completely surrounding many grains, while with others it has gone 
farther, and found its way to the centre along the cleavage cracks. This 
mineral occurs in its usual form in scales or sheaves, and is easily dis- 
tinguished by its high double refraction, small extinction angle, and 
strong pleochroism, the ray vibrating parallel to the long axis being 
dark green, while that vibrating perpendicular to this direction is either 
ereen or bright yellow. It is probable that the uralite further changes 
to chlorite ; but since biotite was generally to be found in the vicinity 
passing into chlorite, it could not be definitely determined. The distri- 
bution of the calcite shows that it is derived from the pseudomorphism 
of the augite, as well as from the decompositon of the feldspar. 
Compact green and brown (basaltic) hornblende, though noticed once 
or twice, are extremely rare. 
The biotite when present is generally either in plates, from its pene- 
tration of feldspar and augite, clearly original, or in fine scales or aggregate 
masses in association with augite. The former variety contains inclu- 
sions too small to be determined, with the characteristic pleochroic zones 
