348 



GEOLOGY 



Changes of surface. Circular surface openings or basins are 

 sometimes developed during earthquakes. This was the case dur- 

 ing the Charleston earthquake of 1886, 1 and similar effects have 

 been noted elsewhere. These openings often serve as avenues of 

 escape for ground-water, gases, and vapor. They are commonly 

 supposed to be the result of the collapse of caverns, of other sub- 

 terranean openings, or the compacting of rock, the collapse often 

 causing the forcible ejection of water. Such openings are likely 



Fig. 283.- 



Sand cones and craterlets observed after the earthquake of 18G1, 

 in Greece. (Schmidt.) 



to be formed only where the surface material is incoherent. Sand 

 cones and craterlets are sometimes developed (Fig. 283). During 

 the California earthquake of 1906, the ground was much broken 

 along the line of the fault which caused the shock (Fig. 284). 

 Earthquakes sometimes dislodge masses of rock in unstable posi- 

 tions, as on slopes or cliffs, and occasion slumps and landslides. 



Effects on drainage. The fracturing of the rock may interfere 

 with the movement of ground-water. After new cracks are de- 

 veloped or old ones opened or closed, the movement of ground- 

 water adapts itself to the new conditions. It follows that springs 

 sometimes cease to flow after an earthquake, while now ones bivak 

 out where there had been none before. The character of the water 



1 Button, Ninth Ann. Kept., U. S. Geol. Surv., pp. 209-528. 



