The New York herald., 1870-05-06
Views Of an Expert.

To THE EDITOR OF THE HERALD:-
1t has been suggested from several sources, and
among them in the HERALD, that the removal Of
Blossom Rock in San Francisco harbor by chamber
ing under the rock and blowing it up by heavy
mine Of powder at single explosion, should afford
hint for the removal Of some Of the rocks at Hell
Gate. comparison Of the two situations will give
us some light on the subject. Blossom Rock was in
the open harbor or bay of San Francisco. Tie two
nearest points are Meigs' wharf, nearly nile, and
Alcatraz light, nearly mile and a quarter distant
yards from Ha.etts Point to Wards Island. Vessels
could avoid Blossom Rock, while Hell Gate Is often
%n eoa e YeSea
passing through this narrow channel with
n a0s single % hour ,dt Blossom Rex 1s was
surface at low tide, comparatively level and uniform
IN surface, ana porous friable sandstone, easily
penetrated. NO currents 0tRer than an ordinary
tide swell in space so broad ana open. In He'll
Gate the rock Is granite, with heavy seams OF
quartz, and In some places paraking Of the texture
and hardness OF gneiss.
A current sweeps over these rocks, rough Jagged
and seamy, at a rate OF eight and hall miles an
hour giving the appearance OF u huge mill.race as
the water dashes in whiris aud eddies over and be-
yond the rocks. The depth OF this fierce current
most OF the channel rocks is from fourteen to
twenty feet at low water. Now, even were 1t posi-
Die; on one OF these ragged rocks, at such depth
and car W sac @ drs 70 @ place eH an = iron IN a rd
80 as to exclude the water from the inside,
how long Is toars Radss to suppose
would come in contact with itS And If
twenty to nifty men were excavatlng the shaft within
such cylinder would not the slightest collision
make watery burial for every soul OF them? Does
the public wish such calamity This plan Of re.
moving submarine rocks is really not g. novel
one wit With y. San Francisco As early as Noysm,
The feasibility Of such a plan for Halett's Point
This is the most practicable If not the only pracu
cable place in Hell Gate for such procedure Here
we have promontory running out from the land
and dipping down under the waters OF the channel.
wooden Golfer dam has been constructed against
the shore upon the part Of the rock bare at low
water. Within this dam the rock is being excavated
the same as quarTying on land. When level COR
responding TO twenty-five feet below low water has
Ueen reached IL Is proposed by General Newton 10
try how Tar galleries for powder mine under the
remainder Of the reel can he made available or
AS to the time aud cost of removing subaoueous
rock Dy THIS method, 1t Is certainly much slower and
generally twice as expensive as drilling and blast
ing III detal Ii situations where both processes are
The removal OF Blossom Rock shows this in part.
In The early part OF March, 1869, Colonel Williamson
United states Engineer at San Francisco, sent me
detailed plan and profile drawing Of Blossom Rock.
with view OF obtaining bid forlts removal. Bids
were TO be opened April 15 1862 The matter passed
b asst would take place In April OF this year. II am
correctly informed there was available for the re-
Inoval OF this rock S1500O0. 1t is stated that
cIoic feet OF rock were excavated from within the
cofter dam, making 4S2 cubic yards and tnat five
months were consumed in doing 1t. Six months of
time previous to this or from the 10Th OF May 1892
must be added for preparation. This amount OF
rock has been removed from Halletts Point IN
period OF six weeks, and 1t Is certainly within the
compass of single apparatus, IN detail drilling and
twenty-five feet nnder the water f,0Oo cubic yards
per month, even under the unequaed Qlnicult!es Of
Hell Gate and at cost per cubic YARD one nall that
save 70 ihe government ct least $4,000 600 il carry
Hs s fDNEY MS 4 T. ggEESsoRN H