740 WALTER HARVEY WEED 
Quartz Monzonite} Granodiorite Adamellite 
po Landsberg 
t ; i 
ae Siem aiNerni Pyramid Peak Vereen 
Rosenbusch 
Sip ieerccsveeteeeorsieiouss 67.12 66.83 67.45 68.97 
INOS Ges eos a0.o586s 15. 15.24 15.51 14.80 
(GENO aH aios Sareea 3.43 3.59 3.60 3.82 
IMietOVeden caaoou one itey yal 1.63 1.10 1.15 
ISON ican Conon oboe 4.52 4.46 3.66 4.53 
Nas Ol eee Gig ye canoes 2.76 3.10 3.47 2.40 
The close similarity of this rock to the quartz-monzonites of 
the Sierra Nevada is apparent from these figures. It is evident 
from the analyses that the Boulder granite nearly corresponds to 
Brogger’s adamellite. 
THE BUTTE GRANITE 
The Butte granite (or quartz-monzonite) covers an area of sev- 
eral square miles and is the prevailing rock of the Butte district, 
and the one in which the world-famous copper and silver veins of 
that place occur. It is, therefore, of more than ordinary interest, 
and has been carefully investigated in connection with the study 
made of the general and economic geology of the district. It is 
a rather dark colored, coarsely granular rock which is seldom 
seen in conspicuous exposures about the productive mines owing 
to a close sheeting with much decomposition near the mineral 
veins and ready disintegration in other parts of the district. 
Away from the mineralized areas it is well sheeted and forms the 
usual bowlder and castellated forms of such rocks. Its darker 
tone and greenish feldspars render it easily distinguished from 
the bowlder type. Throughout the entire district it is very uni- 
form in appearance, as it proves upon analysis to be in composi- 
tion, though differing somewhat in the relative proportions of 
the constituent minerals. It is also uniform in grain over the 
entire district, but hand specimens show in local patches a varia- 
tion of textures. Inclusions of a much darker and finer-grained 
dioritic rock are often seen weathered in relief on exposed sur- 
faces ; they are always small, seldom over a few inches across, 
angular and rather scarce, never making an appreciable part of 
