San Francisco Bay, accessible by the Golden Gate, is the principal harbor on the Pacific Coast, and is, indeed, one of the most magnificent harbors in the world. It is land-locked, that is, surrounded by a continuous land border except at its entrance through the Golden Gate. Including San Pablo Bay, it has a length of about fifty-five miles, and varies in breadth from three to twelve miles. The entrance to the harbor, however, is impeded by a bar across the mouth of the Golden Gate, over which there is a depth of but thirty feet of water at low tide. San Francisco has over 750 miles of streets, 200 miles of which are paved. The city is lighted by both electricity and gas, and has an extensive system of water-works, the water being brought from the Pilarcitos and Calaveras Creeks, situated from twenty to forty miles respectively from the city. San Francisco is in a region where earthquakes are common. It might, therefore, be visited at any time by a great catastrophe. There have occurred between 1850 and 1888, no less than 254 earthquake shocks in the State of California, these shocks having been especially frequent in the country surrounding San Francisco Bay. The most severe were the earthquake of 1868, which injured San Francisco; the Owens Valley earthquake of 1872; the Vacaville earthquake of 1892; the Mare Island earthquake of 1898; and a smaller earthquake in 1900. Since 1900 there was a period of rest until the 18th of April, 1906. As in the case of practically all severe earthquakes, that which destroyed San Francisco consisted of a few momentary shocks: then all was over. According to a preliminary report of the State Earthquake Commission, appointed by the Governor of California, April 21st, 1906, these shocks, as recorded in the observatory at Berkeley, began at twelve minutes and six seconds after five A. M., Pacific Standard Time. Their entire duration was only one minute and fifty seconds, but, as frequently happens, there were a number of minor shocks, following at regular intervals during the next few hours as well as the next few days. While the most severe shocks were in the neighborhood of the Peninsula of San Francisco, yet minor disturbances were felt as far north as Coos Bay, Oregon, and as far south as Los Angeles, California. As shown by recording instruments at the seismograph station at Washington, D. C., Sitka, Alaska; Potsdam, Germany; and Tokio, Japan, a series of waves were propagated through the earth, as well as over its periphery. The damage done within the city limits was wide-reaching. Among the buildings almost completely destroyed were the City Hall, on which about $7,000,000 had been expended, the United States Post Office, besides many business blocks, hotels, department stores, theatres, banks, churches, and dwelling houses.