128 PROCEEDINGS OP THE CALIFORNIA 



February and March, 1864. 



During the present year, 1864, we have had two smart earthquakes at the 

 date of writing this report. 



February 26th. — At San Francisco a light shock at Oh. 40rn. m., and another 

 at 2h. 10m. m. These were reported to me by persons who were up in the 

 south and west parts of the city. At 5h. 47m. a very smart shock occurred, 

 having three distinct vibrations, which induced many to rise somewhat earlier 

 than was usual. This earthquake was preceded by a strong electric storm (so 

 called here), between this city and Yisalia ; the particulars of which have not as 

 yet all come to hand. It was followed next day by one of those severe " north- 

 ers " with which the people of this State are very familiar. Barometer very 

 low. This fact is mentioned only on account of the unseasonable period at 

 which the gale occurred. 



This earthquake was felt more severe at San Jose and Santa Clara than at 

 this place, and occurred at nearly the same hour. 



March 5th. — A severe shock of earthquake at San Francisco at 8k. 49m. m. 

 The first wave had a north and south direction and continued 1% seconds ; 

 nearly \% seconds elapsed before the second shock, which was at 8h. 49m. 3s., 

 and continued \% seconds. The second shock was rotatory ; the pendulum 

 swinging north and south from the first shock, began and continued to describe 

 a short oval or nearly a circle from the effects of the second shock, and con- 

 tinued thus for more than half an hour, until stopped and brought to rest. 

 Magnetism was not suspended in this earthquake, nor any other that has 

 occurred since my instrument was suspended. These observations were made at 

 the height of twenty feet four inches from the ground. The total of time 

 included in the shock was nearly five seconds. The farthest point south to 

 which I have been able to trace its effects is the Mission San Juan, and north to 

 Sacramento, a distance inclusive of 177 miles. In an easterly direction we have 

 not traced it east of Stockton, about 60 miles. It was felt at Santa Clara, 

 Santa Cruz, Gilroys, south of San Francisco, and at Santa Rosa and Petaluma 

 to the north. 



Since the above was in type, advices have been received from Visalia. At 

 that locality the shock was very smart. The first shock took place at 8h. 45m. 

 m., being four minutes earlier than that at San Francisco. This gives for the 

 entire distance, north and south (over which the earthquake extended), 257 

 miles. This extent of latitude, and the almost simultaneous period of time at 

 which it was observed along the entire line of distance so far as heard from, 

 leads to the conclusion that its probable centre was south of San Francisco and 

 nearly in the same longitude. From the violence of its action I feel inclined 

 to the belief that its centre was in the neighborhood of San Jose, for all 

 accounts agree in this one point, that more turbulence of the earth's surface 

 occurred in this region during its continuance than at any other place yet 

 known. At Visalia the first shock was a mere tremor, but was followed by an 

 undulatory movement when the second shock occurred, which was some three or 

 four seconds later. This wave moved in an east and west direction at that 

 place. 



