THE 
AMERICAN GEOLOGIST 
Vol. VII. APRIL, 1891. No. 4. 
GEOLOGY OF THE MOTHER LODE GOLD BELT.* 
By Harold W. Fairbanks, B. S., San Diego, Cal. 
The term Mother Lode is used to designate a series of gold 
bearing veins, of great magnitude, forming a continuous line over 
a hundred miles long through the counties of Mariposa, Tuolumne, 
Calaveras, Amador and El Dorado, Cal. They usually occur in a 
belt of black slate, with either slate, diorite, diabase, serpentine or, 
occasionally granite as wall rock, and are distinguished by a 
peculiar green vein-matter, known as mariposite, and by the more 
or less ribbon-like character of the quartz. 
As far as can be learned the term " Mother Lode " was first ap- 
plied to the veins worked at Nashville, twelve miles south of 
Placerville, El Dorado county, in the latter part of 1850 or earlier 
part of 1851. 
In the use of the term Mother Lode it is not intended to convey 
the idea of a genetic relation to other lodes or veins, though it is 
likely that, from the size, extent, and richness of this series of 
veins the early miners first used the expression partly with that 
signification, and partly perhaps, meaning the source from whence 
came the great wealth of the surface placers. 
The magnitude of the operations on the Mother Lode gold belt 
since the earliest days of mining in the state and the importance 
of a thorough knowledge of the occurrence of its ores, is best illus- 
trated by the fact that over the whole length of the Lode, 112 
miles, there is an almost continuous series of mineral locations, 
* Condensed from an article on the geology of the Mother Lode 
region in the 10th annual report of the State Mineralogist of California. 
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