GABBROS OF EAST SOOKE AND ROCKY POINT. 
13 
wall rock by hornblende can be observed in all its stages. When 
it is complete, nothing but a felted mass of long-bladed crystals 
of dark green, common hornblende, or pargasite, remains. A 
very small amount of feldspar in minute interstitial grains is 
usually present, but it is doubtful whether it has been deposited 
from the solutions or is simply residual. The middle of the 
small veinlets is usually occupied by a string of magnetite grains 
with some pyrrhotite. 
The very large hornblendite zones are identical with the 
smaller in composition, but differ from them in two important 
respects. They have been affected by faulting movements, and 
the copper ores have been deposited within them. The faulting 
had granulated the large-bladed hornblende crystals, so that 
much of the hornblende of these zones is now no more than 
cemented dust, and has produced numerous slickensided cracks 
and fissures, while at the same time much of the hornblende has 
been converted into chlorite. The solutions which carried the 
copper appear to have ascended . through these fissures and 
deposited chalcopyrite and small amounts of calcite, quartz, 
pyrite, and zeolites. 
The mode of formation of these wide hornblendite zones is a 
matter of some doubt. It seems impossible that alteration could 
have extended to such distances from the walls of a single nar- 
row fissure, since in all the unfaulted hornblendite veins such 
alteration may be observed to extend only a few inches from 
the central joint crack. It seems equally unlikely that these 
zones could originally have been wide, open fissures, since, as 
will be next described, fissures originally only 2 or 3 feet in 
width, have been filled, not with solid hornblendite, but with 
coarse gabbro, grading into aplite at the centre. The most prob- 
able hypothesis appears to be, that these zones represent pre- 
existent, sheeted fault zones which afforded the solutions a mul- 
titude of closely spaced, planes of slip through which to rise, and 
thus gave them power to alter broad bands of country rock. 
Gabbro-aplite Veins. Three or four veins, 1 to 3 feet in 
width, which can be described only as gabbro-aplite veins, were 
