WILSON: MEDLOED DIKE AKEA. 
355 
Granites .— A number of igneous intrusions, older than the breccia 
already noted, succeeded the formation of the sedimentary series, 
coming in, probably, after these had been folded. The earliest of 
these intrusions, in the area under consideration, is that of a horn¬ 
blende granite. 
As shown on the map, granites occur in two portions of the area, 
immediately north of the stratified series north of Hall road, and 
also at the north end. For the most part, these granites are moder¬ 
ately coarse-grained in texture, white to pink in color, mottled with 
green, due to the presence of much epidote as a secondary mineral 
from the alteration of plagioclase and of hornblende. The quartz 
is light in color, translucent, and relatively abundant. The ortho- 
clase feldspar, in the hand specimens, varies from pink to white, 
the salmon colored or pink variety being especially abundant in the 
granite from the more southern of the two areas. The plagioclase 
feldspar for the most part has a low maximum extinction angle 
(about 15°) on the twinning lamellae, so that in composition it lies 
between the oligoclase and albite types. Much of it is altered to 
muscovite, and the contorted twin lamellae in manv cases ffive evi- 
dence of strain. The prevailing color of the plagioclase is white, 
though frequently it is stained greenish by secondary epidote. The 
hornblende, when present, is of a light green color, but for the most 
part it has undergone alteration. 
In the specimens examined, necessarily taken from near the sur¬ 
face, the feldspars, especially orthoclase, and the hornblende were 
almost invariably altered. The chief secondary products from the 
alteration of both feldspars are kaolin and muscovite (the former in 
rather larger proportion), chlorite from the hornblende, and epidote 
from the plagioclase feldspar. The usual accessory minerals, titan- 
ite, magnetite, hematite, and zircon are present in small amounts. 
Tlie epidote, in an amount great enough to give the granite a pale 
greenish tint, often occurs in distinct streaks or veins several inches 
in width, and has a mottled greenish-white appearance. Locally 
pink feldspar and white quartz are arranged in bands. JMore fre¬ 
quently we find dark, almost black, fine-grained portions of the 
mass carrying a large amount of biotite, some magnetite, and a 
correspondingly marked reduction in the amount of feldspar. In 
one instance a drusy cavity within this darker segregation contained 
glassv crystals of quartz and crystals of pale blue fluorite. In 
