66 THE SAN FRANCISCO EARTHQUAKE AND FIRE. 
SLOW-BURNING OR " MILL " CONSTRUCTION. 
Section 99. A building of the slow-burning or " mill " construction type is a 
building whose outside walls are built of masonry, concentrated in piers or 
buttresses, between which is a thin wall containing the door and window open- 
ings, and whose floors and roof are constructed of heavy timbers, covered with 
plank of a suitable thickness ; the girders being supported between the walls 
by posts. 
SOME FEATURES OF THE EARTHQUAKE AND FIRE. 
AMOUNT OF DESTRUCTION DUE TO THE EARTHQUAKE AND FIRE, 
RESPECTIVELY. 
Within the burned area all frame buildings and practically all 
buildings with timber floors were totally destroyed, with all their 
contents. This classification includes mill buildings and those of 
every other type in which the floor construction is combustible. 
Practically all the so-called fireproof buildings Avere gutted, and 
their contents were a total loss. The average loss on the buildings of 
class A was, in my judgment, considerably in excess of the average 
loss on the " fireproof " buildings in Baltimore. This statement can 
not be made with absolute positiveness, however, in the absence of a 
detailed estimate of the cost of repairing each building, which I had 
not time to make. I am quite sure, however, that the damage in San 
Francisco was greater than it was in Baltimore. 
From what was left of the ruins themselves, and from the testi- 
mony of competent observers, including engineer officers who were 
ordered into the business district of San Francisco immediately after 
the earthquake and before the fire had destroyed the evidences of 
earthquake damage, I think it is quite certain that the earthquake 
damage was extensive and severe. There were no available data on 
which to base an accurate estimate, but I formed a general impression 
that the damage done by the earthquake alone was at least as great 
as 10 per cent of the total damage by fire and earthquake combined. 
The damage from the earthquake, however, was localized in a re- 
markable degree. In places a group of buildings were almost totally 
destroyed, and buildings almost in contact with them on all sides 
escaped practically without damage, although I feel quite sure that 
many of the wrecked buildings Avere superior in every way to their 
neighbors which escaped. Owing to the remarkable variation in the 
intensity of the shock from point to point, thus demonstrated, the 
measure of damage done to an individual building is by no means a 
measure of the excellency or inferiority of its construction. Some 
specific evidence on this point is presented elsewhere in this paper. 
FIRE-FIGHTING OPERATIONS— THE USE OF DYNAMITE. 
The fire, of course, completed the work begun by the earthquake. 
(See Pis. LIV-LVII.) The interruption of the water supply, due 
