98 THE SAN FRANCISCO EARTHQUAKE AND FIRE. 
the south it was not of a nature to inspire confidence in its carrying 
power at the depth shown on the foundation plans. He accordingly 
obtained authority to lower the footings wherever the material at 
the depth shown on the plans seemed unreliable, so that the footings 
of the south half of the building were lowered — some of them, as I 
remember his statements, to a depth of 20 feet or more below the 
basement-floor level. At any rate, he carried them to a point where 
the material, in his judgment, was sufficiently hard and compact, All 
this underlying material is very sandy; but at considerable depths, I 
understand, gravel appears, and the combination is almost as hard 
as hardpan. 
The walls, floors, and all parts of the post-office building proper 
are carried on the steel frame. The outer walls consist of a granite 
facing, carried on the steel work at each floor level. The granite is 
not backed up in the usual way. the backing having been omitted 
to save weight. Some distance behind the granite an inner wall was 
built of hollow terra-cotta blocks. The space between the granite 
and the terra cotta was used for the passage of pipes, air flues, etc. 
The granite was heavily anchored to the steel work. In a number 
of panels of the steel work corner braces made of a pair of channels 
were used, and they were fastened as far down on the columns and 
as near to the center of the wall girder that spanned the space 
between the columns as the window openings would permit. There 
was also some portal bracing in a part of the building over which 
it had been intended to erect a tower. This intention was afterwards 
abandoned, but I understand the bracing was in place. In a general 
way, panels of the outer wall in which the corner bracing was used 
suffered less than adjacent panels — especially in projecting pavilions, 
where there was no bracing. 
Practically all the interior w T alls of the building above the base- 
ment were built of hollow tiles. The tiles were of excellent quality, 
with webs nearly 1 inch thick. The floor and roof construction was 
of clinker concrete, reenforced with expanded metal. Suspended 
ceilings of metal lath and plaster were very generally used. In the 
mail-handling room there were a number of isolated columns filled 
solid with clinker concrete and covered with 4 inches of enameled 
brickwork. The column covering was circular, the bricks having 
been made radial for this purpose. 
The lower part of the column, however, was incased in a circular 
cast-iron covering made in halves and put together around the col- 
umn. This casing took the place of the enameled brick up to a 
point above which injury from blows and abrasion was not likely to 
occur. There were also in the mail-handling room a number of 
circular shafts of enameled brickwork, with stairways inside, leading 
to the inspectors' galleries. The corridors of the building and the 
