The Mankato free press. [volume] (Mankato, Blue Earth County, Minn.) 1879-1924, 1894-03-16
SAVING STONE LOGS.
A REMARKABLE MILL OPERATED BN
TEE GEOLOGICAL SURVEY.

Interesting Discoveries Are Made In This
Petrified Lumber NIill-Aids In Making
Up Geological History-The Band Saw
and How 1t Is Worked.
There are many novelties in the govern.
ment departments at Washington, and
| especially in the scientific bureaus. The
most novel that has yet been discovered is
petrifed lumber mill operated by the
geological survey. 1t is an institution that
has not many visitors, it's location down
| in the basement of the survey building on
| + street being rather out of the track of
the regulation sightseer, but there the sur
vey lapidaries grind thin sections of rock
| and minerals of all sorts for microscopic
| examination, and there is band saw, the
| invention of the survey, that will cut any
| thing from hot butter to quartz crystal.
Lately the scientists have been saving
up lot of vegetable petrifactions from
| Idaho. They can carve up anything in the
shape of petrified logs that they can get
in front of their saving machine. Even
the ossified man of the dime museum
would not be safe from them, and indeed,
lately, they were called on to cut up pet
rified woman one that was on exhibition
in Washington. After they had bored into
one of the damsel's lower limbs a little
way they struck gas pipe. The petrified
lady was made out of portland cement,
sud the scientists gave her up as hard
case, which, in fact, she was.
But the most interesting case that has
come to the petrified lumber mill was
known as cycad, a sort of vegetabl par
asite which fourished in the prehistoric
forests of the country some millions of
years ago, before the woolly elephants and
saber toothed tigers had made their APP
pearance in the Businesses of the Rocky
mountains, and even further back than
local traditions are carried in Alexandria.
The cycads were practically an unknown
quantity. The lot sent it was, in fact, the
greatest collection that had ever been gath
cred, some small specimens having beer
secured by the British museum, but moth
ing to compare with the giant 900 pound
one that is now at the National museum.
One of the small ones, weighing 35 or 40
pounds was sent up to the survey to have
uome sections made for microscopic exam
nation. 1t looked very much like cocoa
nut with the husk on and was cut ur
almost as easily as though it had never
been petrifed.
ing more than an endless steel wire be-
tween an eighth and sixteenth of an inch
thick, running at a very high rate of speed
over two good sized tlywheels. Water
and emery are fed on the wire as it runs,
and the saw comes as near being an ire
sistible force as anything known in the
cutting line. Since the invention of the
wire saw in the survey it has been copied
nv m hpp of In tcrip
esta blishments all over the country.
Besides the saw there are a number of
grinding machines, smooth iron plates re-
volving like grindstones fat side up and
flooded with water and emery. On these
plates sections of stone for microscopica'
examination can be ground thousandtis
of an inch or less in thickness, SO as to be
perfectly translucent under strong light
These sections are usually not larger than
10 cent piece, but in examining the cy
cad a section was wanted big enough to
show the plan of cell growth, and slab
was cut almost as large as mans hand.
This, like all of the stone specimens, after
having one side ground perfectly fiat, was
transferred to a glass plate, to which il
was fastened with Canada balsam. 1t
is a very beautiful specimen, showing in
prismatic colors the lines of cell partitions
and annular layers like the rings of a tree
trunk.
The lapidary establishment is one of
the most essential aids that the geological
survey has in working up the geology of
the country. Many of the rocks that are
met within the field cannot be distinguish
ed from each other, except by laboratory
examination, and as the nature of the
rocks filling the different sections of the
country has to be ascertained in working
up it's geological history the specimens,
carefully labeled, have to be sent back to
the department. in Washington for study
and classification.
Three methods are used in the identifi-
cation of the close grained metamorphic
rocks that cannot be recognized on casual
eXaminatiOn-by measuring the number
and angles of the crystals, by chemical
analysis to get at the chemical constitu-
ents of the rock, and by microscopic eX.
animation, when, in the thin sections, the
crystalline structure can be seen and the
chemical constituents recognized by the
aid of polarized light. Some of the thin
stone sections mounted on glass slides are
very beautiful in coloring and crystalline
arrangement, and others are simply curl
Gus. One of the most remarkable is one
VI ZIG IdIS WHICH
has lately been discovered in Arizona, and
is what is known as pleochroic.
When viewed under the microscope, it
seems to be made up of detached crystals
Of deep blue. When, however, the slide is
| turned around at different angle, some
of the blue crystals disappear and others
| spring INTO view.
One Of the minerals, of which there are
several deposits in this country, which are
shown in the geological surveys collection
of slides, is peridotite. This gains interest
from the fact that it is the associate of
! the diamond in all of the great African
! fields. Its finding by Professor Lewis of
Philadelphia in Kentucky some years ago
caused great excitement, and there was
some warm prospecting for diamonds, but
none was ever found It's connection
with the African diamonds came from the
fact that when the peridotite had come to
Che sCrf;.ce in a molten condition it had
been forced through the clefts or faults in
some very rich carboniferous slate fields.
The hot rock had crystallized the carbon
OF the slate measures into diamonds, which
are found scattered along few yards on
each side OF the contact What the dia-
| mOnQ DrOSDectOrS are locking for in this