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POPULAR SCIENCE MONTHLY 



fillings, some of the cracks opened by passing waves do not close again, 

 but remain as permanent vestiges of the shock. Closely associated 

 with these secondary cracks in soft ground are permanent changes in 

 surface form. At the head of Tomales Bay, for example, a broad 

 tract of soft ground between high and low tide was thrown into low 

 ridges, with cracks along their crests, and these remained until de- 

 stroyed by wind waves. In San Francisco considerable tracts of 

 ' filled ' land were shaken together and thus made to settle a few feet, 

 and were at the same time slidden several feet toward the bay (Fig. 9). 

 Certain changes, very conspicuous to the observer who drove about 

 the country, are closely associated with roads. A side-hill road is 



Fig. 7. A Zone of Earthquake Fracture where it crosses a Road near Bolinas. 



usually constructed by excavating a notch in the natural slope and piling 

 the excavated material in an embankment at the outer edge of the 

 notch. In course of time, and especially during rainy seasons, the 

 embankment at the outer edge of such a road settles and has to be built 

 up as a matter of repair. Portions of the bluff on the up-hill side of the 

 notch are also apt to fall away, taking the form of small landslides, 

 which have to be removed from the road as a rule after every rainy 

 season. The earthquake precipitated many changes of this sort. Along 

 all side-hill roads in the immediate vicinity of the rift a crack was de- 

 veloped between the embankment and the original soil against which 



