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POPULAR SCIENCE MONTHLY 



they signify but little. They mean simply that loose soil has been 

 shaken down. They do not go down into the underlying rock. From 

 the true earthquake crack they may usually be known at once, because 

 their course is determined by the topography. They are not straight. 

 The true earthquake rift moves on in straight lines, broadly speaking, 

 careless of topography. But topography is not careless of the earth- 

 quake rift. On either side of it, for perhaps hundreds of feet, the 





RELIEF .MAP 



CALIKOKMA 





'nvK. 





Relief Map ok California. 



rocks are crushed to flinders by the impact and grinding of the opposed 

 Avails. An old fault is therefore marked by an excess of erosion. A 

 valley or saddle marks its general course. Streams choose it for their 

 basins, and when it crosses a mountain the softened rock yields to form 

 a saddle or other form of depression. For these reasons, an earth- 

 quake fault is often marked in California by successions of dairies and 

 of reservoirs. The valleys thus formed are fertile and well watered. 

 For the most part, in much-faulted regions, such as form the rim of 



