ECONOMICAL GEOLOGY. 
237 
also in Polk and Cleaveland ; embracing an area of over 200 square 
miles. 
They appear to cover the greater part of the land, rise often to a con- 
siderable height on the slope of the hills, but are naturally more concen- 
trated in the bottom and flat lands. The gravel beds in this region vary 
in thickness from a few inches to thirty feet, and are covered with soil 
and clay, which is also more or less auriferous, although much poorer than 
the gravel beds below. 
These deposits have been worked since 1830, and befopp gold was 
known in California many thousands of hands were at work digging and 
washing in a rude way, yet many millions of dollars were produced with- 
out the knowledge of a proper use of water. 
Since that time very little has been done.; in some instances the old 
-travel was worked over again, and has made fair returns to the adven- 
turers. 
Yery large tracts of land, containing extensive and valuable deposits, 
have never been touched, and, by the introduction of the Californian hy- 
draulic system of operations, a safe and very profitable business could be 
carried on. 
The gold is rarely found in nuggets ; generally as fine dust and in 
■small grains. Its fineness averages about 825 thousandths. It is associated 
with numerous interesting minerals, such as platinum, diamond, zircon, 
xenotiiae, monazite, and many others. 
Experiments with vein-mining in this region have not proved success- 
ful ; the rich veins are too narrow in width, and of too limited extent in 
•depth, and the large veins do not contain enough gold to be advan- 
tageously worked. 
A small region of valuable gravel beds exists in the gneissoid rocks and 
micaceous slates of Franklin and Nash counties, in the eastern part of the 
state. It has been most extensively prospected at the Portis Mine, where 
it is very rich, and has been worked since about 50 years, having pro- 
duced, it is said, over $1,000,000. 
The productive gravel is here the result of the disintegration of nu- 
merous small granular or sugary quartz veins, and very fine specimens of 
gold in such quartz are frequently met with. 
The fineness of the Portis Mine gold was generally about 985 thou- 
sandths. 
There are enormous gravel piles at the mine — the remnants of former 
operations. 
The gold in the gravel deposits, principally, is the loose gold, which 
had existed in the rocks and between their laminae, or that from the small 
