ISOSEISMALS: DISTRIBUTION OF APPARENT INTENSITY. 233 
The whole periphery of the hilltop was broken into a series of concentric blocks or steps, 
and the outer ones moved down the hill from 2 to 3 feet. The artificial stone work was 
badly cracked and dislodged. These phenomena indicated that the material used in grad- 
ing the upper slopes had settled somewhat, with consequent rupture of the surface and 
wrecking of the building. No other explanation can be urged for such striking damage 
on this hill, in view of the small damage produced on other rock summits in the city. 
All the driveways in the western part of Golden Gate Park showed scattered narrow 
fissures. There were but few structures here, and they did not show significant damage. 
These were low, strong, frame buildings. It is a district which was extensively graded in 
the work of landscape gardening, and is underlain by a deep sand deposit. It appears to 
have suffered a shock of intensity of the middle range of Grade B. 
PHENOMENA OF ESPECIAL INTEREST. 
About the Ferry Building, at the foot of Market Street, is a district of “made” land, 
shown on map No. 17, in which high intensity was manifested. Here buildings of all 
sorts were crowded close together. Wooden buildings, | story to 3 stories high, with brick 
or stone work fronts, were interspersed among ordinary brick buildings from 2 to 6 or 8 
stories in height. Mingled with these was a considerable number of modern, class A, 
office buildings. Here the fire burned fiercely and caused great havoc, heaping the streets 
and the cellars of buildings with fallen brick and stone and twisted beams and girders. 
For weeks after the conflagration many of the streets were completely hidden under the 
débris. So much of the damage due directly to the shock was thereby concealed or ob- 
literated, that no adequate knowledge of the direct effects of the earthquake could be 
obtained in this part of the city; tho eye-witnesses tell of cornices and gables which fell, 
and of walls and roofs which collapsed at the time of the shock. After the fire had past, 
standing walls revealed ugly, sinuous cracks, in rudely parallel systems, which were not 
due to fire nor to dynamite. Masonry blocks in the walls of excellent modern buildings 
were broken as by a blow. Rivets were sheared off in parts of the framework of steel 
structures, and tension rods in such frames were badly stretched. Tubular cast-iron 
columns, supporting floor girders, were broken off near their bases in cellars where they 
rested upon piling. The concrete casing of piles was frequently broken. Wherever the 
intensity was high, the tendency to crack or crush near the base, as tho a sharp blow had 
been struck there, was notably conspicuous. In spots the streets sank bodily, certainly 
as much as 2 feet, probably more. Accompanying this depression, concrete basement 
floors were broken and arched, as if to compensate for it. The surface of the ground was 
deformed into waves and small open fissures were formed, especially close to the wharves. 
Buildings on the water side, along East Street, generally slumped seaward, in some cases 
as much as 2 feet. The damage was greatest close to the water’s edge, growing less as the 
solid land was approached, gradually at first, then more rapidly. These phenomena 
seem to suggest that the materials used in filling were shaken together so as to occupy less 
space with the accompanying development of waves, fissures, and structural damage 
The more recent the filling, the more it would be compacted; hence the greater prevalence 
and magnitude of destructive effects near the water’s edge. 
As well as could be made out from the inadequate evidence left by the fire, the district 
which suffered intensity of Grade B is limited on the landward side by a line drawn from 
Filbert Street to Market Street, between Battery and Front Streets; thence between 
First and Fremont Streets to a little south of Folsom Street, where the line turns and 
runs eastward to the wharves. Flanking this district on the landward side is a narrow, 
sinuous area limited by a line drawn from Filbert Street to Green Street, Just east of San- 
some Street; thence between Sansome and Montgomery Streets to Market Street; thence 
to the corner of Mission and First Streets; thence between First and Fremont Streets 
