. After earthquake and fire . and property-lines which cross the rift are amount of dislocation varies. In several instances ob-served it does not exceed six feet. A more common measure-ment is eight to ten feet. In some cases as much as 15 or16 feet of horizontal displacement has been observed, whilein one case a roadway was found to have been differentiallymoved 20 feet. Probably the mean value for the amount ofhorizontal displacement along the rift line is about ten feetand the variations from this are due to local causes such asdrag of the mantle of soil upon the rocks, or t
. After earthquake and fire . and property-lines which cross the rift are amount of dislocation varies. In several instances ob-served it does not exceed six feet. A more common measure-ment is eight to ten feet. In some cases as much as 15 or16 feet of horizontal displacement has been observed, whilein one case a roadway was found to have been differentiallymoved 20 feet. Probably the mean value for the amount ofhorizontal displacement along the rift line is about ten feetand the variations from this are due to local causes such asdrag of the mantle of soil upon the rocks, or the excessivemovement of soft incoherent deposits. Besides this generalhorizontal displacement of about 10 feet there is observable inSonoma and Mendocino counties a differential vertical move-ment not exceeding four feet, so far as at present known,whereby the southwest side of the rift was raised relativelyto the northeast side, so as to present a low scarp facing thenortheast. This vertical movement diminishes to the south-. 154 AFTER EARTHQUAKE AND FIRE. east along the rift-line and in San Mateo county it is scarcely,if at all, observable. Still farther south there are suggestionsthat this movement may have been in the reverse direction,but this needs further field-study. The great length of the rift upon which movement has oc-curred makes this earthquake unique. Such length impliesgreat depth of rupture, and the study of the question of depthwill, it is believed, contribute much to current geophysicalconceptions. The time of the beginning of the earthquake as recorded inthe Observatory at Berkeley was 5 hr. 12 min. 6 sec. a. m.,Pacific standard time. The end of the shock was 5 hr. 13 sec. a. m., the duration being 1 min. 5 sec. Within an hourof the main shock twelve minor shocks were observed byS. Albrecht of the Observatory and their time accuratelynoted. Before 6 hr. 52 min. p. m. of the same day thirty-oneshocks were noted in addition to the main disturbance. Thes
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