GROUND-WATER 



207 



dissolved from a given place. Instead of making the rock porous, 

 in the usual sense of the term, large caverns may be developed 



Fig. 166. Diagram to illustrate the form and relations of caverns developed 

 by solution. The black spaces represent caverns. Limestone sinks 

 are represented at the surface where the roofs of caves have fallen in. 



(Fig. 166). In their production, solution may be abetted by the 

 mechanical action of the water passing through the openings which 

 solution has developed. 



Fig 167. Sections of petrified logs, near Holbrook, Ariz. Beds probably 



Jurassic. 



