168 
IOWA ACADEMY OF SCIENCE 
Avide angle the alternate occurrence of the bonanzas would be the natural 
arrangement. A careful study of the relationships of bonanzas to geo- 
logic structures would doubtless yield practical results of the highest 
importance in the future exploration of the district. 
The vertical grouping of the bonanzas into distinct upper and lower 
zones, as is generally recognized by the miners of the district, I do not 
attach much importance to. Any such arrangement, if it actually exists, 
must be manifestly accidental in that it cannot be dependent upon geo- 
logic structure. Singularly enough, hoAvever, such lodes as the Cristo 
for example displayed bonanzas only in the upper portions. On the 
other hand the Santa Gertrudis, Vizcaina and others presented them only 
in th e de pths. A few veins, as the Corteza and Analco are reported to 
have contained bonanzas in both upper and loAver zones. 
In this connection it may be of interest to note that a single bonanza 
in the San Rafael mine yielded more than $15,000,000. This rich body 
Avas 3,000 feet long, 1,200 feet deep, and from 5 to 10 feet in thickness. 
