ISOSEISMALS: DISTRIBUTION OF APPARENT INTENSITY. 211 
very severe. This continued for about 10 seconds, and then came a swaying motion, 
that seemed at right angles to the first. 
A chimney stack, of brick, 120 feet high, belonging to the power-house on the Home 
- grounds, was shattered. Its rectangular faces fronted to the northeast, southeast, south- 
west, and northwest, respectively. In two places, one about 40 feet and the other about 
60 feet from the ground, the upper portion of the stack was shifted, as if the rotation were 
from north to west to south to east, it being understood that the motion of the earth 
was in an inverse direction to that of the twisted distortion of the chimney. The westerly 
corner hardly moved while the easterly corner was shifted several inches. The lower 
fracture had a displacement of about 2 inches at the easterly corner, and the upper 
fracture had a similar displacement. In the dispensary of the Home, the first portion 
of the shock threw the bottles from the shelves upon northwest and southeast walls. 
The latter portion of the shock precipitated the bottles from the other walls. This was 
proven by finding articles from the northeast and southwest shelves lying on top of those 
from northwest and southeast shelves. 
Napa State Hospital. — The effects of the earthquake are thus described in the Cli- 
matological Report of the U.S. Weather Bureau for April, 1906, by Mr. W. H. Martin: 
At 5" 14™ a. m. on the morning of April 18, 1906, a severe earthquake commenced, and 
lasted about 80 or 90 seconds. The apparent motion at the beginning was from the west 
by south to the east by north, a rolling motion for about 15 to 20 seconds, then a light 
interval for a few seconds, then a renewed force of a twisting nature, intensity IX. The 
ground, to the eye, seemed to be quivering; the hills seemed to have a rocking motion, the 
trees seemed to be shaken by the hands of a giant; everything lookt to be in motion; the 
air was hazy and still. Many brick and stone walls were thrown to the ground and others 
damaged to such an extent that they will have to be taken down. Nearly all chimneys 
were thrown down, and of those standing some are turned a quarter way round. Milk in 
pans was thrown out in an easterly and westerly direction. The estimated damage to the 
city of Napa is about $150,000. The damage to this institution was very light, except 
that the main tower will have to come down. 
Napa (E. C. Jones). — The damage to street gas mains at Napa was very slight, only 
two leaks developing. The gas station was badly shaken up; about 10 feet of the end 
wall of the brick building was thrown down, falling on top of the boiler and breaking off 
the steam pipes. The gas-holders were badly shaken. Water was displaced from the 
tanks, but only one guide wheel was shaken out of place. 
Wooden Valley, Napa County (H. W. Chapman). — On level alluvial ground near the 
base of the surrounding hills, no objects were overthrown. There were 2 maxima in 
the shock, of which the first was the strongest, the movement being north and south. 
Pope Valley, Napa County. — The top of one very old chimney was thrown over, 
falling to the south. Another was cracked, and 4 or 5 bricks from the top of another fell 
down into the fireplace. 
Mr. H. P. Gordon reports that he was in Pope Valley at the time of the earthquake, and 
that the shock awoke him. It seemed to be a tremor at first, then an oscillatory motion 
east and west. It seemed to him as if his bed were a gold pan, and he were being panned 
out. His house stands on rock. 
Berryessa Valley, Napa County. — The shock is reported to have been quite heavy on 
the level land of the valley-bottom. 
Vallejo, Solano County. Population 8,000. (W. D. Pennycook.)—The shock was quite 
as hard as that of 1898, when the brick structures at Mare Island navy-yard were very 
much damaged, some of them having to be taken down. The vibrations in that earth- 
quake were lateral, nearly north and south. The vibrations of the earthquake of April 
18, 1906, while equally severe, were different in character. In Mr. Pennycook’s house are 
2 mantels facing north and south, and a large china closet. In the earthquake of 1898 
every article on both mantels was thrown to the floor, and in the china closet the crockery 
