Los Angeles herald., 1890-05-17
They Will Tell Where Gold
May be Found.
A New Departure of the Geo.
logical Survey.
No More Searching at Random for
Rich Finds.
How Rocks are Analysed by the Depart.
ment at Washington-Microsc
Photographs Taken.


vey at Washington are preparing maps
on large scale, showing the exact spots
in California and elsewhere in this
country that give promise of producing
gold. These are intended for use by
prospectors, who have heretofore worked
at random.
1t is generally supposed that gold is
only found in stray places and isolated
localities, whereas the fact is that it is
the most widely distributed of all
metals. Every gravel bank and sand
bar is a mine of it, the only trouble being
that there is not enough of the metal
present to pay for the process of separat-
ing it. There is not CARLOAD of sand
on the Pacific slope that will not yield at
least "color," says report recently
issued, and Los Angeles is built on a
soil that would very nearly pay for the
panning just for the gold in it. The
yellow mineral is everywhere almost,
and why?
Simply because all of it found in the
world was originally deposited by sea
water during those ages when the waves
of oceans overhowed the continents.
Under certain chemical conditions sea
water will dissolve gold and hold it in
solution, and thus it happened that dur
ing the epoch referred to the ocean was
tincture of this metal. Gold was one
of the elements entering into the origi-
nal composition of the forming earth
crust, and the sea water held it sus-
pended for a time and finally deposited
it, as if with the intention of putting a
coat of gliding on the globe. But in
some places conditions were more favor
able than in others for the reception of
the deposit. For instance, the Califor-
MIA hills in the process of formation
were, by causes geological, all crumpled
up, so that cracks were left everywhere,
to be filled up with whatever the sea
water had to precipitate. In these
cracks and fssures, in the course of CEN
turies, gold collected with other miner
ais deposited in the same way, and IN
this manner were formed what are now
called gold-bearing veins. Such of the
gold thus concentrated as was washed
down by rivers and torrents that ate
away the hills was found loose in the
soil or in the beds of the streams, while
what remains in the rocks must be got
out by mining and crushing.
1t is believed by biologists that all the
gold in the earth is on the surface of the
globe, or very near it, it being found that
the supply dwindles to nothing after
mining operations have reached very
moderate depth. Quite otherwise is it
with silver, which was all thrown up
originally from the earths bowels by
volcanic action. Just as occurred in the
case of the gold, the floods of ocean took
up the silver and deposited it wherever
circumstances were favorable, as in Ne
vada, where one silver-bearing crack in
the rocks at VIRGINIA City has already
been mined to the depth of 200 feet
without getting anywhere near the bot
tom. This is the largest body of silver
ore ever discovered, with the exception
of one in Peru, Mining at this great
depth is carried ON with the utmost
difficulty, owing to the heat.
The processes employed by the geo.
logical survey in the examination OF
rocks are most interesting. To begin
with, chip OF the stone to be investi-
gated is ground down on one side with
an emery-wheel until it is an absolute
plane, perfectly polished. The polished
side is then attached to piece of glass
and the other side of the stone chip is
applied to the emery-wheel until tn,
chip itself is ground all away, save onl,
a film of inconceivable thinness that re
mains stuck upon the glass. This film
is finally removed with great care ant
placed upon little glass ''slide" of tn
sort used for objects to be inspected il
the microscope. Another piece of glass
very thin, is placed over it, the tive
glasses being stuck together securely
and now the stone is ready to be exam
ined.
For this purpose it is put under ;
powerful microscope, in which an ar
rangement is provided for polarizin
light. Looked at through the instru
ment in the ordinary way, the film Q
stone, which resembles mere blot O
discoloration on the glass to the nakeC
eye, is exhibited merely magnifet
enormously. But when by the turn of
screw the light is polarized, the objec
is suddenly dressed in the most gorgeou
colors of the rainbow, each elemen
found in the rock taking on hue of it
own-brilliant blue, red, green or wha
not. Thus the study OF the stone ant
its constitution is rendered compare
lively easy.
But this is by no means all. 1t is de
sirable to retain these pictures, and 70
this purpose photographs are taken 0
the little film of stone with micro
camera-a wonderful instrument tina
makes very much magnified pictures 0
the objects. A strong ray OF artifcia
light is made to pass through the glas
slide with the rock-flm attached oit, tn
same ray continuing in straight lin
through the tube of a microscope into tn
camera, the position Of which CORE
spends to that of the eye observing tn
object. A very much enlarged pictur
of the stone-tilm is made on the DIR
plate and is subsequently printed lik
any other photograph. 1t only remain
now to paint the photograph with waite
colors precisely as the same object al
pears to the eye through the microscope
with the aid of polarized light, and yo
have permanent picture record OF ths
particular kind of rock.
Something happened the other da
that shows one use of practical sort
which the study of rocks may be pu
Out in the wild west a mail bag VIZ
emptied of valuable contents by partit
unknown and filled with stones. III
loss was not discovered until the bs
reached its destination, and no one ha
any notion where the theft was commi
ted within thousand miles OF journe,
- l. 4 t.faa af.al