SALUBRITY. 135 



ty or generally, preceded the shocks, nor is there any rule 

 by which we can predict their occurrence, nor have we any 

 instrument by which we measure precisely their duration, 

 violence, or the course of their vibrations. 



99. Their Frequency. Earthquakes are common in some 

 parts of California, and especially at San Francisco, Los An- 

 geles, and near the Tejon Pass, at the southern junction of the 

 Sierra Nevada and Coast Mountains. They are rare at Sacramen- 

 to, Marysville, Vallejo, and Napa. As a general rule, they are 

 less frequent and less severe in the northern than in the southern 

 part of the State. The vicinity of Humboldt is more often shak- 

 en than any other place north of the Bay of San Francisco. 

 About a dozen earthquakes are felt in a year at different places 

 in the State ; not so many at one place. Most of the shocks 

 are so slight as to pass unnoticed by a great majority of the 

 people ; and there are persons who have resided six or eight years 

 in San Francisco, and many who have resided ten years in 

 other parts of the State, and say they have never felt an earth- 

 quake. No strongly-built house has been injured, by an 

 earthquake in California, north of latitude 35, since the Amer- 

 ican conquest. Several brick walls have been cracked in San 

 Francisco, but they were weak structures, built on " made 

 ground," and would, perhaps, have cracked by settling, of 

 their own weight. Large four-story houses have been so much 

 shaken, that the inmates have run out in great alarm ; but, on 

 examination, it was found that the buildings were uninjured, 

 even in the slightest perceptible manner. 



On one such occasion, a gentleman, who thought his life in 

 great danger, and ran to save it, observed, before he left his 

 room, that the water was splashed out of his basin by the 

 movement of the house. The basin was of earthen-ware, 

 about fifteen inches in diameter at the top, six inches deep, half 

 full of water, and it stood on an ordinary wash-stand. He 

 supposed that, with another such a shock or two, the building 

 must be in ruins ; and he was very much astonished to find 



