CRANE. | 
Developing Mineral Properties 
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Fig. 8. The Mathews lease on the Bonanza land. 
to the workings, although there is no regularity in their ar- 
rangement. 
Even when the whole rock mass is so thoroughly 
impregnated with ore as to warrant the milling of it all, 
pillars are left during the removal of the larger part of the 
ore, and then robbed, when the ore has been exhausted, or 
left as permanent supports. 
When much barren rock oc- 
curs, or where the ore is sparsely disseminated through the 
rock, it would probably be better to leave the pillars, although 
partially composed of ore,'as permanent support. 
however, seldom done. 
This is, 
If any ore is visible on the sides of 
the pillars, they are generally robbed. This method is modi- 
fied somewhat when soft, water-bearing formations are met. 
The plans of underground workings as shown in figures 
8 and 9 will give an idea of the irregularity of the method 
of working in hard ground. The dotted lines represent 
183 
