National Republican., 1883-11-06
THE ROCKS IN THE RIVER.

Progress BEING Made in Their Removal
One Hundred and Flny-six Tons Al
ready Blown Up.
The American Dredging company, of Phila-
ddphia, the contractors for removing tho rocks
dangerous to navigation in the Georgetown
harbor, arc making considerable progress in
their work. There were four groups of these
rocks in the harbor. on each one of which
vessels have run at different times and sus-
tanned more or less damage As soon as these
rocks were discovered buoys were placed over
them, but rs these have generally disappeared
with each breaking up of the ice, and as the
vessels now engaged in coal carrying are OF
much heavier drnught than formerly, con-
gress made an appropriation some years ago
to have the harbor carefully surveyed and
these rocks exactly located Upon the report
of the survey further appropriation was
made for their removal
The company above named were the lowest
bidders for the work and received tho con-
tract. The rocks TO he removed are situated
as follows: First 800 feet from the Aqueduct
bridge, in front of tho Borden Coal and Iron
companys wharf; second, opposite tho tail
race of Herr & Cisselps Columbia mills
third, $50 feet southwest of the Potomac
boat house; fourth, oil q street wharf, and
quite close to the shore.
A depth of twenty feet, at low tide, was TO
tractors have removed the first group to the
required depth, and are now Mt work OH the
second and for the prosecution of the work
have q most complete outfit. The boat on
which the workmen live is provided with a
large boiler, supplying steam to two engines,
one of which drives the drill, the other the
air pump which supplies air to the divers
while at work on the bottom of the river.
The boat is moored to movable frame work
made by four heavy spuds being lowered TO
the bed Of the river, on which is laid plat
form, carrying the machinery for working
the drill, the position of the whole being
changed from time TO time as required by
four anchors leading from each corner, and
attached to long hawsers. two and one
half inch steel drill is used, and is placed in
proper position and watched by the diver at
the bottom OF the river, aud when the tap is
made in tho rock to the depth of about two
and n half feet tin can of tho above
dimensions, loaded with dynamite and
tightly stopped with cork, through which
runs wire, connected with the firing bat
terry on the boat is placed in the top by the
diver, who is quickly hauled aboard the boat
and the electric spark from the battery fires
the cartridge. The report of the explosion is
not much louder than that made by the dis
charge of an ordinary shot gun, but the effect
upon the water is very great and strongly
perceptibe for a good distance to any one in
row boat communicating to it a vibratory
motion, and causing to its occupants the same
sensation that would be produced by tho boat
running on tightly strung wire.
Immense bodies of rock are torn loose
at each explosion, the larger pieces being
slung in chains by tho diver and hoisted
into stone scow. Some of these pieces
have been raised weighing rs much
as five TONS The smaller pieces are left
on the bottom of the river until after the
blasting is completed when a dredging ma
chine will be used for scooping them up. The
amount of solid rock removed so far is in the
neighborhood of sixty-five cubic yards, weigh
ing about $50 TONS
On the completion of this work, and the
dredging Of the channel, on which two steam
dredges are now at work, there will be no
danger of getting aground or running on
rocks to the largest class of coasting vessels
engaged in the coal trade, although some of
those now trading to Georget own carry up
ward of 700 tons of coal