Berkeley is on the east shore of San Francisco Bay 10 miles northeast of San Francisco. This view shows one of the wide cracks that was made in the hills near Berkeley at the time of the San Francisco earthquake of modern times. The most violent shock occurred about 5 o'clock in the morning. Many lesser shocks came during the day. The greatest force of the shock was in and around San Francisco. Much damage was done also at San Jose and Santa Rosa. Buildings were wrecked, and great fires raged for three days. The quake had broken the water mains and made it hard for the firemen to gight the fire. About 500 lives were lost. Property valued at over $500,000,000 was destroyed. But as soon as the quake was over and fires were put out, rebuilding began.

It is not known exactly what causes earthquakes. But it is believed that the chief cause is the shrinkage of the earth. We are sure that parts of the earth's interior are highly heated. As these portions cool, shrinkage takes place. This affects outer layers so that great cracks are formed and the folds of the earth are changed. In Japan, for example, tracks have been twisted out of shape so that they wind like snakes. In the earthquake at Madrid in 1811, in some places great stretches of land were thrown up, and in other places the land was sunk so that water covered it. When an earthquake occurs in any section, its vibrations spread in all directions. Its effect is somewhat like dropping a stone into still water. The heavy waves are nearest the point where the stone falls. As the waves spread from the center they become weaker.