The Indianapolis journal. [volume] (Indianapolis [Ind.]) 1867-1904, 1894-05-06

Then the surveyor takes a plane table.
now. q plane table Is a board attached TO
the Top OF a tripod, upon which IL Is
movable horizontally and may be clamped
IN any position. 4 sheet or paper is fast
shed 10 this board upon which the map is
70 be constructed, and upon this sheet are
plotted carefully all the primary points
whlch have been determined. There Is an
other and very essential instrument con-
nected with the plane t~able-what Is known
as the alidade. This consists Of q ruler
upon which. fastened rigidly to il. is a
telescope, The surveyor sets up his plane
table over one OF the signals which has
been located, sets the ruler Of his alidade
upon the line connecting the position OF
THIS signal on the paper with the position
of a neighboring one. and turns the plane
table around until the neighboring signal
appears in the middle of the field Of the
mat instrument. The table is then ''ori-
ented,' as ii is called. and he clamps IL In
position. Then with his alidade he sights
upon numerous other points and toward
each OF these points he draws a line uDon
the paper. Then he visits a neighboring
primary point. sets up his plane table and
offents II as above, sights and draws lines
70 those points which he sighted from the
flrst station. The intersection OF these lines
locates the point in each case. In this way
he goes over the area to be surveyed and
locates. IL may be. hundreds Of points in
Inls graphic manner directly upon the
TRANERSING VS.. CHARACTERIZATION.
There is another method of location
" 0CNdilos lndl >
what is known as traversing. All roads
are surveyed by traversing. This differs
radically from the method above described.
which is triangulation, in the fact that
instead of measuring two angles and thus
locating a point, the surveyor measures a
direction apd a distance. thus locating
them; and he carries forward a chain of
such direction and distance measurements
running from one triangulation point TO
anotner. checking by his error of closure
upon the second point. By these two meth
Jus vast numbers of points are located ali
over the area under survey, covering the
sheet quite closely. There may be a score
OF such points in each square inch of the
nap: Moreover. these are as a rule picked
salient points in ACCOMPLISHMENTS or
NILS, functions of streams. etc.
& When ine map has reached this stage
II Is ready for the sketcher. who is COM
monty the most experienced topographer
IN the party. He takes the sheet with this
data upon 1T and goes over the ground
sketchlng In the features OF the man. the
Toads and railroads. the houses. contour
ntn Wnich represent relief. streams. etc.
elc. All this work Is done in the field.
using the country itself directly as copy,
anu the sketch thus made is the finished
tered before completion. The linking is
done in the evenings or on
rainy days, since If it We're left to the
end o. the season the pencil marks might
be illegible. The original draft of the toIo.
graphic map being completed. it is en-
graved upon copper and a small proof edi-
ton is printed.
The topographic map is a necessary pre-
urinary to accurate geologic work. When
the Topographic base has been printed il
is placed in the hands of a geologfst, VINO.
thus equipped, proceeds to trace out the
relations of the different rock tons
as they appear at the surface within the
limits of the map, deIineating the djsIribu-
ton of all formations. The result Is a
geologic map. The biologists work differs
the region in which lie is operating. and
the time required for the study of the ge-
ology of any atlas sheet depends more upon
the nature of the geology than upon the
size of the sheet. In some regions il is
possible for the geologist to survey a. thou
sand square miles in less than two months;
IN other regions he annot accomplish the
same task in less than three or four years.
mus the cost of the geological work per
square mile varies widely and Is controlled
Dy the facts OF the geology. The geologist
pursues his work as a scientific study
which is TO be applied to the economic de-
velopment of the resources of the region.
The mineral deposits of any region have
formed during the development of certain
rocks with which within that region they
the origin and distribution OF the minerals
Is related TO the origin and occurrence OF
these rocks. 1t may therefore happen that
the geologist studies broad areas barren
of valuable minerals in order that he may
better understand the reasons for the oc-
currence of the minerals in certain local
tiles. 1t follows that a large part of his
work appears to the layman to have no
practical application, and the geologist MIN
self, during the course of his study, may
not foresee whar its ultimate economic
value may be; vet the results of geology
abundantly testify to the Importance of
studies into the mineralOgic and geo.
logic relations of the rocks. AS an
instance of this the recent results of geo.
logic studies Of the Marquette iron region
OF Lake Superior may be cited. The iron ore
formations of that district produce more
than half the iron now used in the United
States Mines have been worked for many
years, and the region has been Thoroughly
proSpected so far as the appearance OF the
iron-bearing formations at the surface have
justified the practical miner in proceeding
with his Investigations. A few years ago
biologists began 10 study in the already
developed mines the conditions of occur
renee of the iron ores and the relations of
the associated rocks. As a result of that
study they AVE developed the principle
that these iron ore bodies have been formed
by the deposition of the iron ore from a
solution in water flowing down the surface
of an imperviOuS stratum under the ground
and meeting with other subterranean waters
carrying oxygen. This simple generalization
has enabled them, after a very careful study
of the general geology of the region, 10
point out in the vicinity of districts that
have been worked for many years and were
supposed TO be thoroughly known localities
where bodies of iron ore are likely to be
found. but where they had previously not
even been suspected; and it is probable that
the application of the scientific results of
that survey will add many millions of tons
VI NdlttdDit = III ItSOuICtS OF
the region.
The geologic maps, together with the topo-
graphic map. are published in the geologic
atlas of the United States. This is the great
work for which the survey was organized
and toward which ii has been striving since
it's inception. Each atlas sheet, covering
usually about one thousand square miles,
Will be published by itself. with proper de-
scriptions. and in the form of the topo-
graphic and geologic maps. The explana-
tons of the maps and the descriptions are
written in popular language, avoiding the
use OF technical terms, so that they may
be available TO others than the trained ge-
ologist. and the purpose of the work is to
place the results OF the survey within the
reach of the people OF the country. This
publication is but just begun. and the num-
Der of atlas sheets now available in fOlics is
very limited. They will be printed as rap
idly as the means supplied to the survey
permit. and will be distributed as generally
as circumstances allow. L. CT.
DeIirious Social Amusements.
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