The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1894-01-26

oo', weighing Gnlrby-HVe or forty
pounds, was sent up to the Survey to
have some sections made for microscopic
examination. 1t looked very much like
coeoanut with the husk on, and was
cut up almost as easily as though it had
| never been petrified
The band saw used in the work is
nothing more than an endless steel wire
between an eighth and sixteenth of
an inch thick, running at a very high
rate of speed over two good-sized Nv
wheels. Water and emery are fed on
the wire as it runs, and the saw comes
as near being an irresis tible force as
anything known in the cutting line
Since the invention of the wire saw in
the Survey it has been copied by num-
Der of laboratories and lapidary estab-
lishments all over the country.
Beside the saw there are a number of
grinding machines, smooth iron plates
revolving like grindstones fat side up
| and flooded with water and emery On
these plates sections of stone for micro
scopical examination can he groun a
thousanth of an inch or less in thick
ness, so as to be perfectly translucent
under strong light. These sections are
unusually not larger than Decent
piece, but in examining the cycad 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 glass plate, to
which III was fastened with Canada hal
sam. IL is now being ground down for
study. 1t is very beautiful specimen,
showing in prismatic colors the lines
of cell partitions an annular layers like
the rings of tree trunk.
The lapidary establishment is one of
the most essential aids that the GeoIog-
lcal Survey has i'll working up the geo.
logy of the country. Many of the rocks
that are met within the field cannot be
distinguished from each other, except by
laboratory examination, and as the ma
ture of the rocks filling the different sec
lions of the country has to be ascertained
IN working up it's geological history, the
specimens carefully labelled, have to be
sent back to the department in Washing
ton for study and classification.
Three methods are used in the identi-
hcation of the close-grained metamorphic
rocks that cannot be recognized on cas-
ual examination, by measuring the num-
Der and angles of the crystals, by chemi-
cal analysis to get at the chemical con-
stltuents of the rock, and by microscopic
examination, 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
| uhLA oucuO SCCOlOuS IuOuDUOu Oll SldSS
slides are very beautiful in coloring and
crystalline arrangement, and others are
simply curious. One of the most remark
able is one of the rare minerals, dumor-
lite, which has lately been discovered in
Arizona, and is what is known as pleo-
choric.
When viewed under the microscope it
seems to be made up OF detached crystals
OF deep blue. When, however, the side
is turned around at different angle
some of the blue crystals disappear and
others spring into view. The explanation
is that when the light rays pass through
the crystal cells parallel to their long
axes, there is no interference with the
rays, but the light striking the crystals
at right angles to the long axes, the blue
rays are INSTRUCTED and give color to the
mass. This is only one instance of the
peculiarities by which the various rocks
are recognized.
One of the minerals, of which there
are several deposits in this country,
which are shown in the Geological Sur
vey's 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
Prof. Lewis of Philadelphia in Kentucky
some years ago caused great excitement,
and there was some warm prospecting
for diamonds, but none were ever found.
Its connection with the African dia-
monds came from the fact that when
the peridoitte had come TO the surface
in a molten condition it had been force
through the clefts or faults" in some
very rich carboniferous slate fields The
hot rock had crystalized the carbon of
the slate measures not diamond, which
are found scattered along few yards on
each side of the contact. What the dia-
mond prospectors are looking for in this
country is combination Of peridotite
and :carboniferous states. Whether they
will find it or not is a question.
One of the many searchers after arti :
ficial diamonds lately made an important
discovery that is being utilized by the
survey and by many manufacturing es-
Establishments where abrasives such as
emery and diamond dust are in use The
new substance is known as carborundum
and is the result of passing strong cur
rent of electricity through mixture of
powdered carbon and fine sand in a
closed retort. The chemist did not get
diamonds for his trouble, but he may
yet wear them, as the new compound
promises to prove very valuable and may
pos bly, supplant emery in mauy COM
mercial uses. Washington Post.
The Evolution of the Cuckoo.