OUTLINE OF PRINCIPAL RESULTS. 9 
The ore-filled fissures in the andesite and limestone resulted from 
the cooling of the andesite mass, which developed stretch fractures 
within the 'mass and pulled it away from the limestone wall as a cast- 
ing away from the mold. Where the ore-bearing solutions reached 
the unaltered limestone rather than the silicated contact phase of the 
limestone the ore replaced the limestone. Where they reached the 
overlying quartzite they filled fractures. 
A considerable secondary concentration may be traced to the 
Tertiary lavas which once covered the ore deposits. The ores were 
coarsely recrystallized and chalcedony was introduced as a gangue 
material in place of calcite. No heavy silicates were introduced. 
The concentration under the influence of the lavas is a relatively 
shallow one, which can be fairly separated from the deep primary 
concentration. 
The entire effect of weathering is not known, because the ores have 
been observed only above water level. Above this they are porous, 
suggesting that there may have been a considerable amount of solu- 
tion of the gangue materials down to this point. Calcite has obviously 
been leached near the surface and deposited farther down; apatite 
has been altered to osteolite; small amounts of sulphides have been 
oxidized and partly removed; limonite has developed in thin films 
along the margins of cavities and along fissures. In general, how- 
ever, the obvious relations of the characteristics of the ore to con- 
ditions other than weathering seem to indicate that the iron oxides 
themselves have been little affected by weathering. 
Inferences as to the extension and shape of the ore deposits in 
depth are drawn from a consideration of origin. The ores may 
have a considerable depth. The ores are not likely to be so thick 
along the contact on upper slopes, because gravity tended to close 
the openings formed by the cooling of the andesite mass. There 
seems to be no reason why ore should not be found at the limestone- 
andesite contact at places where the contact is now overlain by 
Cretaceous quartzite. 
The Iron Springs deposits are typical of many other western iron- 
ore deposits, and it is believed from personal observation that their 
origin has essential features in common. Description is made of the 
structure of ore of similar occurrence in the adjoining Bull Valley 
district, and reference is made to deposits regarded as belonging to 
the same class in other parts of the West. 
