EARTHQUAKES AND SEAQUAKES 



85 



in its downward movement, the effect is to compress the porous 

 layers and so force the contained water upward along the joints to 

 the surface, carrying with it large quantities of the sand (Fig. 77). 



. 79. One of the many craterlets formed near Charleston, South Carolina, 

 during the earthquake of August 31, 1886. The opening is twenty feet across, 

 and the leaves about it are encased in sand as were those upon the branches 

 of the overhanging trees to a height of some twenty feet (after Button), 



Ejected at the surface this water appears in fountains usually 

 arranged in line over joints, or even in continuous sheets, and the 

 sand collecting about 

 the jets builds up lines 

 of sand or mud cones 

 sometimes described as 

 "mud volcanoes" (Fig. 

 78). The amount of 

 sand thus poured out 

 is sometimes so great 

 that blankets of quick- 

 sand are spread over 

 large sections of the 

 country. Most fre- 

 quently, however, the sand is not built above the general level 

 of the surface, but forms a series of craterlets which are largely 



FIG. 80. Cross section of a craterlet to show the 

 trumpet-like form of the sand column. 



