. ISOSEISMALS: DISTRIBUTION OF APPARENT INTENSITY. 213 
Other observations mentioned by Professor See which are indicative of the intensity of 
the shock are the agitation of the water which was thrown into sharp cones, and filled with 
bubbles due to the escape of gases from the underlying mud; the shaking of trees and tele- 
graph poles as by astorm; the fright noticed inall personsand animals; the throwing down 
of unstable objects; the raising of dust from the ground, and the formation of a mist in a 
few places. ‘The motion was not so violent that one could not stand, yet during the violent 
part of the disturbance walking was difficult. All objects had a hazy outline, owing to the 
rapidity of motion, and it is said that persons presenting this aspect offered a comical sight 
to the beholder. The forests were agitated as by a violent wind, and at first the motion 
of the trees was ascribed by some marines on watch to a rising storm. 
Vallejo Junction (T. J. J. See). — This station is just across the straits from the south- 
eastern end of Mare Island and has only a few houses, the injury to which was not at all 
considerable. The intensity here was about the same as at Mare Island and Vallejo, as 
might have been expected from the proximity of these places. 
St. John’s Quicksilver Mine. — At the St. John’s Consolidated Quicksilver mine near 
Vallejo, the following observations are recorded by Mr. Alphonso A. Tregidgo, manager 
of the mine. The note is of special interest as this is the only case in which underground 
disturbances have been observed in mines as a result of the earthquake of April 18: 
We felt the shock about 5" 15™ a. M., first north and south, and then east and west. We 
are working only two shifts, and as the night men “come off” at 4 A.m., there were no men 
in the mine when it occurred. 
Our main tunnel is 1,135 feet in from the mouth. It cuts the lode 367 feet below the 
croppings, and crosses N. 3° 30’ E. At the end of this tunnel the old shaft was sunk 
230 feet deep (vertical). The first 130 feet was thru the lode, the remaining 100 feet 
being in the “‘foot”’ or west wall, the lode going down to the east of the shaft. Within 
the year preceding the earthquake a new shaft was sunk which this main tunnel intersects 
500 feet nearer its mouth, 160 feet below the surface. Right at this point the effects of the 
earthquake appear in the tunnel. The posts of the sets were ‘“snapt off’? about 8 inches 
from the bottom, and forced north for several sets. Our tunnel is timbered thruout 8 x 8, 
sets 4 feet apart. The old shaft timber sets dropt on the east side from 2.5 to 3 feet. This 
shaft is double compartment. The wall plates are north and south, and end pieces east 
and west. Carrying the ends with them, the east wall plates dropt to the 180-foot level, 
so that all the sets above that level are now 2.5 feet low on the east side. (From a point 
1,125 feet in the tunnel the center of this shaft is located 22 feet 5 inches E. 17°8.) We 
have repaired the tunnel, but the shaft is beyond repair. As we connected our new shaft 
with the old shaft workings below the main tunnel level on April 16, just two days before 
the earthquake, we fortunately have no need of the old shaft for working purposes, tho it 
will be necessary to keep it open a while for ventilation. Strange to say, our new shaft was 
not damaged at all. It is timbered from top to bottom nearly 400 feet; sets 4 feet apart, 
close lagged. Not a lagging even moved. From a point 610 feet from mouth of tunnel, 
the center of new shaft bears 8. 76° 30’ W. 14 feet 9 inches. No doubt considerable 
change has been caused by the earthquake in the old workings above the main tunnel, as 
our airways needed repairing in places. 
Benecia (T. J. J. See). — The earthquake was decidedly more severe here than in Vallejo; 
2 or 3 houses collapsed and half, or more than half, of the chimneys were thrown down. 
Major Benét, U.S. A., Commandant of the U.S. Arsenal, informs me that he reported to 
the War Department over 20 chimneys on the Government houses in the military reserva- 
tion either thrown down or so injured that they had to be taken down. These houses all 
stand on solid high ground, none of them being on land made by the filling in of loose earth. 
Some of the Government buildings were cracked and otherwise injured, but on the whole 
the damage was not very extensive. In Major Benét’s residence the furniture was con- 
siderably deranged, books were thrown down, bric-d-brac overturned and some of. it 
broken. Such objects as dishes were frequently shaken off the shelves and crashed upon 
the floor. 
At the entrance to the Arsenal grounds, the Gate House, used for the guard, is a round 
tower about 12 feet in diameter, made of brick and lined with a wooden ceiling. It was 
