312 ELEMENTARY GENERAL SCIENCE CHAP. 



carbonate, being insoluble in water alone, is deposited as soon as 

 the carbon dioxide escapes. 



Stalactites and Stalagmites. The streams traversing limestone 

 districts become saturated with carbonate of lime. In their 

 course they often trickle through crevices in the roofs of caverns 

 which have been formed in the limestone by the same solvent 

 power of this particular water. The drop of water, which is 

 thereby exposed on the roof, is subjected to evaporation, and 



FIG. 142. Stalactites and Stalagmites in Clapham Cave, Lancaster. 

 From a photograph by Mr. George Fowler. 



the escape of the carbon dioxide and loss of water cause a slight 

 deposition of carbonate on the roof, which is continuously added 

 to by a constant succession of drops, until eventually beautiful 

 pendants of calcium carbonate are formed, called stalactites, 

 sometimes coloured by the presence of traces of iron oxide, 

 and often having a wild profusion of forms (Fig. 142). Further 

 evaporation of the water takes place on the floor of the cavern, 

 giving rise to layers of the same chemical compound, called 

 stalagmites. 



