ii 4 POPULAR SCIENCE MONTHLY 



be possible to say definitely whether the original displacement involved 

 the territory on both sides of the fanlt or on one side only. 



A further cheek is to be afforded through the observations for as- 

 tronomic latitude at Ukiah. The observatory at Ukiah is between 

 25 and 30 miles in a direct line northeast of the fault. In connection 

 with the general dislocation it was presumably moved toward the south- 

 east and its latitude diminished by several hundredths of a second. 

 This is one of an international series of observatories established in 

 approximately the same latitude but in different longitudes, for the 

 purpose of determining variations in the position of the earth's axis 

 of rotation. If the observations at Ukiah were studied, alone it might 

 not be possible to separate the result of a small change in the observa- 

 tory's position from the effects of the migration of the axis; but by 

 combining the Ukiah data with those furnished by the other observa- 

 tories of the system, it is probable that the effects of the two causes can 

 be discriminated. 



The most important practical results of the various earthquake 

 studies will probably be afforded by the engineers and architects, and 

 will lead to the construction of safer buildings in all parts of the 

 country specially liable to earthquakes; but the geologic studies of the 

 State Commission are not devoid of economic bearings. In the city of 

 San Francisco and adjacent parts of the peninsula on which it stands 

 the underlying formations include several distinct types, and the dis- 

 trict is so generally occupied by buildings that the relations of the 

 several formations to earthquake injury can readily be studied. Such 

 a study is being made with care and thoroughness, and one of its results 

 will be a map of the city showing the relation of the isoseismals, or 

 lines marking grades of intensity, to tracts of solid rock, to tracts of 

 dune sand in its natural position, to upland hollows partially filled by 

 grading, and to old swamps, lagoons and tidal marshes that have been 

 converted into dry land by extensive artificial deposits. The informa- 

 tion contained in such a map should guide the reconstruction and 

 future expansion of the city, not by determining the avoidance of 

 unfavorable sites, but by showing in what areas exceptional precau- 

 tions are needed, and what areas demand only ordinary precautions. 



Another economic subject to which the commission may be expected 

 to give attention is what might be called the earthquake outlook. Must 

 the citizens of San Francisco and the bay district face the danger of 

 experiencing within a few generations a shock equal to or even greater 

 than the one to which they have just been subjected? Or have they 

 earned by their recent calamity a long immunity from violent dis- 

 turbance? If these questions could be answered in an authoritative 

 way, or if a forecast could be made with a fair degree of probability, 

 much good might result; and even if nothing more shall be possible 



