120 



PHYSICAL GEOLOGY 



of the copper, lead, zinc, iron, gold, and silver, occurring as 

 veins or otherwise, was scattered widely through the neigh- 



FIG. 111. Calcite veins in volcanic tuff. West of Kincraig Point, Elie, 

 Fife. (H.M. Geol. Surv.) 



boring rocks, usually in the form of some compound, and 

 was dissolved, concentrated, and deposited in its present 

 position by percolating waters. Deposits made in caves are 



interesting, but of little 

 importance. Those which 

 extend downward from 

 the roof, icicle fashion, 

 are stalactites; those 

 which are built upward 

 from the floor are stalag- 

 mites (Fig. 112). In cer- 

 tain arid parts of the 

 West, ground water as- 

 cends to the surface and 

 is evaporated there, leav- 

 ing the material which it 

 held in solution as an 

 incrustation which in 



FIG. 112. -Stalactites and Stalagmites laceg coverg j areag 



in Marengo Cave, Ind. (U.S. Geol. 



Sun.) Ground water some- 



