212 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
was thrown from the shelves. On April 18, 1906, nothing was thrown from the mantels, 
but a clock, which in 1898 had been thrown to the floor, was turned around about 20°. 
The postmaster of Vallejo reports that the city is on a hillside adjoining the Mare 
Island strait. The surface is rolling and has very little level land except such as has been 
cut down, which is entirely of clay and soft rock (shale). Sandstones and shales are the 
underlying rocks, and these come close to the surface except along parts of the edge of 
the strait. ‘There was a noticeable decrease in the violence of the shock toward the 
middle, then an increase in severity, the latter part being the stronger. The movement 
was north and south. Objects hanging on gas fixtures by ribbons wound themselves up 
on the same. The Post-office clock stopt. The floors appeared to rise and fall. All 
the damage done was to chimneys; not a brick wall showed any injury. The greatest 
damage was done in the lower levels, the hills suffering very little. 
(T. J. J. See.) —Vallejo is built on hard ground and did not suffer very severely from the 
earthquake. The best estimates obtainable showed that about one-tenth of the chimneys 
were knocked down, or so broken loose that they had to be taken down. The shock was 
not so severe as that of 1898, which was much more local in character. No house in 
Vallejo fell, and chimneys were about the only fixt objects thrown down. Various ob- 
jects in the houses were overturned, such as bookcases, bric-A-brac, and dishes on shelves ; 
and the plastering was somewhat cracked. In general, however, the injury was not 
creat. 
- Mare Island (T. J. J. See). — The earthquake was much less severe than that of 1898, 
which wrecked many of the Government buildings in thenavy-yard. Noneof the Govern- 
ment buildings was wrecked this time, nor was the damage at all serious except in the case 
of two or three new buildings recently erected on the ‘‘made”’ land near the water-front. 
Here the ground was thrown into violent undulations, and the buildings were so twisted 
that about $2,000 worth of repairs had to be made. On this soft ground the brick walls 
were cracked, but as the buildings have steel girders, no part of them fell except one or 
two top-heavy cornices. But the swaying of the brick walls tied together with steel 
frames caused the walls to be cracked and scaled off near the steel supports. In the case 
of the older buildings resting on hard ground, no cracks were formed, nor any injury 
reported. No chimney on Mare Isiand was thrown down, and only one or two were 
broken loose at the roof so that they had to be taken down. The amplitude of the vibra- 
tions in the soft ground at Mare Island was found by measurement to be 2 or 3 inches. 
This was determined from the displacement of the loose dirt around the piles supporting 
the steel frames of the buildings on the ‘‘made”’ land. On the whole, the intensity was 
about the same at Mare Island and Vallejo. 
Prof. T. J. J. See contributes the following note on the swaying of a smoke-stack 
at the navy-yard on Mare Island: 

“This smoke-stack is made of steel, bolted together in sections and lined with fire-brick 
150 feet high and 6 feet across at the top. Three separate witnesses, standing at nearly 
equal angles about the base, and something like 100 yards away, observed the tower writh- 
ing and twisting during the earthquake. The motion was described as like that of a cork- 
screw. All the witnesses say that the top of the stack vibrated in a circular or elliptical 
manner, thru a space of at least 2 diameters; that is, one diameter on either side from the 
mean position. The stack is built on hard ground, and bolted to a heavy brick foundation. 
The motion, therefore, gives the wave distortion of the solid earth, a motion of 6 feet at the 
top corresponding to a wave distortion of one-twenty-fifth part of the radius, or 2° 3’. 
If the stack be regarded as vibrating about its center of gravity, the angle will be about 
half as large. These figures correspond to the distortion of the earth’s level surface pro- 
duced by the passage of the earthquake waves thru the rocky crust.” 

* This appears to involve the assumption that the stack was rigid, which is inconsistent with the 
described corkscrew motion. A. C. L. 
