164 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
a noticeable and important feature of that district, is not found. ! 
The country rock over large areas is a generally coarse though varia- 
ble granite of a red or gray color, frequently cut by small dikes of 
pegmatite. Minor areas are covered by diorite of a variable charac- 
ter. Though usually massive, as observed in limited outcrops, both 
the granite and the diorite, when considered in a broad way, show 
banded structures, due to a more or less evident parallel arrangement 
of the constituent minerals, and to the separation of light and dark 
minerals into narrow plates. These variations are most noticeable in 
areas where the granite preponderates, and in this rock the variations 
range from light-colored siliceous phases to very dark-colored basic 
types containing a large amount of mica and hornblende. Certain of \ 
the dark bands intimately connected with the granite can be distin- j 
guished only with difficulty from the diorites which occur in larger 
independent masses. The structure of these massive diorites is ty pi- j 
cally gneissic, and outcrops which are not banded are rarely observed. I 
DEVELOPMENTS. 
Nine prospects showing the presence of copper minerals in encour- j 
aging quantities were visited. These have been developed by from 
50 to 200 feet of workings. Two days were devoted to a rapid exam- 
illation of the phenomena presented, and these observations form a 
basis for the notes which follow. 
In every case where limonite or iron oxide was found at the surface 
this material has proved to be only a shallow capping; and the zone 
carrying oxides and carbonates of copper beneath it, when present! 
at all, has been unimportant. In no instance did any property vis- 
ited fail to show unaltered pyrite and chalcopyrite at a moderate 
depth from the surface, but there are as yet no thoroughly developed! 
deposits, though on every hand intelligent efforts were being made to 
prove the value of the various discoveries. 
Big Creek shaft. — The property of the Big Creek Mining Company I 
lies northwest of Pearl at a distance of about 2-J- miles. The general 
character of the country rock in the vicinity is granite-gneiss, but 
there are frequent bands of diorite which vary from gray to almost 
black, with changing proportions of hornblende and feldspar. The; 
granite normally contains mica, but locally this mineral disappears 
and certain fine granular streaks in the granite have the appearances 
of being quartzite, though in fact they are made up of quartz 
and feldspar. The country rock at the shaft is a granite-gnei 
which contains more than the usual amount of mica. The workings 
were filled with water and therefore not accessible, but from the 
direction of the shaft the course of the vein seems to be about 
N. 00° W. The vein is said to stand nearly vertical for a distance 
of 100 feet from the surface, and then to dip about 70° S. to the 
bottom of the shaft, which is 145 feet deep. From the material 
