"The turn in the direction of the fire endangered for a time the great Ferry House, at the foot of Market Street. While the section actually destroyed is not, geographically speaking, much more than one-third of the city limits, yet it is in the heart of San Francisco, and includes the chief business streets and the Mission District, inhabited by poor people, and a large part of the so-called Nob Hill Quarter, where were the finest and costliest residences of the city. Another fine residence section, Civic Heights, escaped, together with that known as the Western District. "The unburned district, though large in extent, was in the nature of suburbs, and was not closely built up, so that estimates made, as late as Saturday, declared that three-fourths of San Francisco's improvements in real estate had been destroyed." The burnt district was about two miles from east to west and from two to four miles from north to south, with, of course, very irregular outlines. Naturally, the great destruction wrought by the earthquake of April 18th, 1906, attracted the almost universal attention of scientific men especially interested in earthquake phenomena. We are, therefore, able to speak authoritatively about the probable causes. The great San Francisco earthquake of April 18th, 1906, appears to have been a _tectonic_ quake. Ransome, in an article entitled, "The Probable Cause of the San Francisco Earthquake," says: "The region thus amply fulfils the conditions under which tectonic earthquakes arise. It is in unstable equilibrium, and it is cut by long northwest faults into narrow blocks which are in turn traversed by many minor dislocations. Under the operation of the unknown forces of elevation and subsidence, stresses are set up which finally overcome the adhesion of the opposing walls of one or more of the fault fissures; an abrupt slip of a few inches, or a few feet, takes place and an earthquake results. The region extending for some hundreds of miles north and south of the Bay of San Francisco may be considered as particularly susceptible to shocks on account of the number and magnitude of the faults and the evidences that these furnish of very recent slippings and the marked subsidence in the vicinity of the Golden Gate." CHAPTER XXIX SOME OTHER NOTABLE EARTHQUAKES It would, of course, be impossible within the limits of this book to attempt a description of all the remarkable earthquakes in the annals of science; but before leaving this part of the theme a brief account of a few more among the many may be worth while.