weed.] ORE DEPOSITS AT BUTTE, MONT. lib 
The rocks of the entire district are traversed by a multiplicity of 
joints and fractures. These belong to three well-defined systems, as 
may be seen in excavations in the city or, more clearly still, in the 
great bowlder outcrops to the northeast where the veins are seen to 
be merely mineralized fissures, the exceptional instances in which 
the fractures have been channels for mineralizing solution. In the 
copper area the rocks are intersected by a multitude of fissures* 
which near the surface are filled by quartz and iron oxide, with 
rotted or disintegrated granite between, soft enough to yield to the 
pick. In depth the lesser fractures are not filled and are therefore 
less conspicuous. 
The veins of the district, both copper and silver veins, belong to 
three distinct systems. The oldest lodes have a general east- west 
course, the Parrot, Anaconda, and Syndicate lodes being examples. 
Another set of fractures has a northwest-southeast course, and lias 
displaced the earlier veins. A still later set has a northeast course 
and has displaced both the earlier systems of veins. The first two 
systems are heavily mineralized; the last shows a little endogenous 
ore, but the material mined is mainly the ore broken off from earlier 
deposits and included in the fault debris. This discrimination of the 
I different vein systems and the recognition of the faulting of one set 
by the other and of the resulting mineralization is the result of the 
study of the district made since the Butte folio was published. It 
has been made possible by the enormous development work expressly 
made to develop the structure and continuity of veins for the various 
lawsuits between the mining companies. 
The silver veins surround the copper lodes on the north, west, and 
southwest. Their course and geologic relations are very similar to 
those of the copper veins, but their structure and mineralogic charac- 
ter are different. The silver veins contain sulphide of silver, blende, 
pyrite, and a little galena, and commonly contain no copper save near 
the border of the copper area, where, though occasional bunches of 
copper ore occur, it consists of chalcopyrite and more rarely still tetra- 
hedrite, minerals which occur rarely and very sparingly in the copper 
lodes. The gangue consists of quartz with rhodonite and rhodochro- 
site, and shows marked banding and crustilication, in strong contrast 
to the structure of the coj)per veins. These silver veins form very 
prominent outcrops, the quartz being stained black by manganese 
oxide. The veins are largely due to the filling of open fissures, and 
show but slight alteration of wall rock. They are displaced by and 
traversed by faults with friction breccias and alteration clays like 
those in the coi>per area. 
THE COPPER VEINS AND MINERALS. 
Several of the copper veins were, as is well known, at first worked 
as silver veins. The upper portion of the veins consisted of quartz 
