102 THE SAN FRANCISCO EARTHQUAKE AND FIRE. 
in the post-office were built of 6-inch terra-cotta blocks, with webs 
nearly 1 inch thick. They were beautifully built, every joint being 
absolutely filled with cement mortar that was much harder than 
the tiles, though the latter were of exceptionally good quality. None 
of these walls were thrown down, but many of them showed the 
intersecting diagonal cracks that are characteristic of earthquake 
action. The tiles along the lines of the cracks were so badly shat- 
tered that many of them will have to come out. As a contrast, 
reference is made to PI. XLVI, B, showing earthquake damage to 
good brickwork. In the tile wall the same cracks appear, but the 
tiles are badly shattered for some distance on either side. In addi- 
tion, in much of the flimsy tile work in the commercial buildings 
the adhesion of the mortar in the entire partition, if there was any, 
was destroyed. In the concrete Avails at Palo Alto a few cracks ap- 
peared here and there as a result of the earthquake; but they were 
even sharper and narrower than the crack shown in PI. XLVI, B, 
and there was no shattering effect whatever. 
The column coverings in the mail-handling room, described above, 
were absolutely uninjured, but the circular brick walls around the 
spiral stairways developed many rather ugly spiral cracks. Such 
cracks were very conspicuous also in circular smokestacks, where the 
damaged work was not thrown down entirely. 
The floor construction in the post-office was absolutely undamaged 
by the earthquake. This was one building where " cinder concrete " 
was made as it should be — of well-burned clinker only. In the court 
room which burned out a part of the furred ceiling came down, ex- 
posing the floor slab above. It may not have received a very severe 
test, for when work is done as well as it was in this building even a 
furred ceiling will exhaust the fury of a fairly hot fire. Be that as it 
may, the floor slab showed no signs of damage .whatever, and it was 
the only case I saw where the heat had evidently reached the floor 
slab without leaving some degree of damage behind. The fire did 
not get through the 6-inch hollow-tile walls either, and it took off 
very few exposed webs. Here again it is probable that the plaster 
finish was so well done that it prevented the tiles from getting the full 
effect of the. fire. The fire was stopped at the entrance to another 
court room, where there was a double wooden door, consisting of 
one door on each side of the partition. Water and wet blankets 
sufficed to stop the fire at this point, and it is reasonable to suppose 
that the extra resistance of a second door, even though it was of 
wood, was a material factor in the result. From a purely technical 
point of view it is to be regretted that the post-office building was not 
more seriously involved in the fire, for its fireproofmg was of a com- 
mercial type — in its best possible form, however. Such a test would 
have yielded more interesting results than all the rest of San Fran- 
