128 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
hundred feet apart. The western one is wholly in the metarhyolite of 
Bully Hill; the other, near the surface, is within the dike of meta- 
basalt, and farther down follows the contact between the metabasalt 
and the metarhyolite more or less regularly to a depth of about 500 
feet. 
The walls are sometimes sharp, but at many places are indistinct, 
grading into the material of the shear zone. 
Ore bodies. — The ore bodies occur very irregularly distributed in 
shear zones and range in size from lenticular or sheet-like nodules less 
than an inch in diameter to hundreds of feet long and up to nearly 
a score of feet in thickness. The crushed rock in the shear zone is 
not always mineralized, but generally it is more or less richly impreg- 
nated with ores, sometimes to complete replacement. In the Copper 
City workings, where these features are well displayed, the small ore 
nodules are chiefly zinc blende, with small amounts of pyrite and 
chalcopyrite. 
One of the most important matters concerning ore bodies as they 
lie in the shear zone is that their longer axis usually pitches steeply 
to the north, so that when an ore body is struck the general position 
is a guide to its prospecting. 
Zones in large ore bodies. — Near the surface each large ore body is 
naturally divided into three zones. Beginning at or near the surface 
with the zone of oxidation, where the material is generally known as 
gossan, it passes downward into the zone of enrichment, Avhere the 
so-called black oxides of the miners occur, and finally at greater 
depths into the zone of the original sulphides. These zones are often 
extremely irregular, but are generally well defined. 
Zone of oxidation. — The gossan of the Bully Hill ore bodies is, in 
the main, porous limonite, occasionally with small caves containing 
beautiful stalactites of the same mineral. It results from the altera- 
tion of the pyritous ores, from which nearly everything but the iron 
has been carried away by percolating waters, leaving the iron in the j 
form of a hydrous oxide — limonite. The gossan usually contains also 
a larger portion of the gold of the original ores, but the copper is 
mostly carried down to form rich sulphides in the next zone. It may 
combine with carbon dioxide and give rise to the green and blue car- 
bonates of copper, or be reduced and native copper result. All of 
these ores and also native silver occur locally in the lower part of thel 
gossan or upon the borders of the Bully Hill ore bodies at greater! 
depths. The red oxide (cuprite) rarely occurs at Bully Hill, but, 
according to Mr. Oxam, the mine superintendent, a mass several feeti 
in diameter was found in clay 6 feet from the ore body at a depth of 
151 feet. The bottom of the gossan is very irregular, extending fan 
down into the ore bodies along fissures favoring oxidation. On gentle 
slopes it usually extends 70 or 80 feet below the surface, and some- 1 
times much deeper, but upon steep slopes the gossan may be nearly 
